feat(web): floating live preview + per-plugin "Preview on display", drawer a11y

Preview-while-configuring:
- Floating mini preview (fixed, bottom-right) available on every tab except
  Overview, fed from the same SSE display stream by updateDisplayPreview -
  no new connections. Collapses to a round toggle button; open/closed state
  persists in localStorage; hides on Overview where the full preview lives.
- "Preview on display" button on every plugin config page header: runs that
  plugin on the real display for 60 seconds via the existing
  /display/on-demand/start API and opens the floating preview, closing the
  configure -> see-the-result loop.

Drawer/nav accessibility:
- aria-current="page" tracks the active tab (system + dynamic plugin tabs,
  matched via their Alpine @click expression), updated from the activeTab
  watcher so search deep-links and checklist navigation are covered too.
- Escape closes the mobile drawer and returns focus to the hamburger;
  opening the drawer moves focus to its first tab.

Validation: all 40 web tests pass; Jinja parse + div balance on both
touched templates.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KEZK1P1Q1fu5pcuVrkrCFZ

web_interface/static/v3/app.css

@@ -1356,3 +1356,38 @@ button.bg-white {
 [data-theme="dark"] .power-warning-banner-dismiss {
     color: #fca5a5;
 }
+
+/* ===== Floating live preview (all tabs except Overview) ===== */
+.floating-preview {
+    position: fixed;
+    right: 1rem;
+    bottom: 1rem;
+    z-index: 70;
+    background-color: #111827;
+    border: 1px solid #374151;
+    border-radius: 0.5rem;
+    box-shadow: 0 8px 24px rgba(0, 0, 0, 0.4);
+    overflow: hidden;
+}
+.floating-preview img {
+    background-color: #000;
+}
+.floating-preview-toggle {
+    position: fixed;
+    right: 1rem;
+    bottom: 1rem;
+    z-index: 70;
+    width: 44px;
+    height: 44px;
+    border-radius: 9999px;
+    background-color: var(--color-primary);
+    color: #ffffff;
+    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.35);
+    align-items: center;
+    justify-content: center;
+}
+@media (max-width: 640px) {
+    .floating-preview img {
+        width: 192px !important;
+    }
+}

web_interface/static/v3/app.js

@@ -379,6 +379,104 @@ document.addEventListener('DOMContentLoaded', function() {
     });
 });
 
+// ===== Floating live preview =====
+// A mini preview of the display, available on every tab except Overview
+// (which has the full-size one). Open/closed state persists per browser;
+// frames arrive via the existing SSE stream (updateDisplayPreview in
+// app-shell.js feeds #floating-preview-img).
+window.toggleFloatingPreview = function(open) {
+    try { localStorage.setItem('ledmatrix-floating-preview', open ? '1' : '0'); } catch { /* no-op */ }
+    window.updateFloatingPreviewVisibility();
+};
+
+window.updateFloatingPreviewVisibility = function(tab) {
+    const panel = document.getElementById('floating-preview');
+    const toggle = document.getElementById('floating-preview-toggle');
+    if (!panel || !toggle) return;
+    let active = tab;
+    if (!active) {
+        const el = document.querySelector('[x-data]');
+        const data = el && el._x_dataStack && el._x_dataStack[0];
+        active = data && data.activeTab;
+    }
+    const onOverview = active === 'overview';
+    let open = false;
+    try { open = localStorage.getItem('ledmatrix-floating-preview') === '1'; } catch { /* no-op */ }
+    panel.style.display = (!onOverview && open) ? 'block' : 'none';
+    toggle.style.display = (!onOverview && !open) ? 'flex' : 'none';
+};
+
+document.addEventListener('DOMContentLoaded', function() {
+    window.updateFloatingPreviewVisibility();
+});
+
+// Run a plugin on the real display for 60s via the existing on-demand API
+// and open the floating preview so the effect is visible while configuring.
+window.previewPluginNow = function(pluginId) {
+    fetch('/api/v3/display/on-demand/start', {
+        method: 'POST',
+        headers: { 'Content-Type': 'application/json' },
+        body: JSON.stringify({ plugin_id: pluginId, duration: 60 })
+    })
+    .then(r => r.json())
+    .then(data => {
+        showNotification(data.message || ('Previewing ' + pluginId + ' for 60 seconds'),
+                         data.status || 'success');
+        if (data.status === 'success') window.toggleFloatingPreview(true);
+    })
+    .catch(err => {
+        showNotification('Preview failed: ' + err.message, 'error');
+    });
+};
+
+// ===== Nav accessibility =====
+// aria-current tracks the active tab. Buttons are matched by their Alpine
+// @click expression ("activeTab = '<tab>'"), which works for both the static
+// system tabs and the dynamically injected plugin tabs.
+window.updateNavAriaCurrent = function(tab) {
+    document.querySelectorAll('.nav-tab').forEach(function(btn) {
+        const expr = btn.getAttribute('@click') || btn.getAttribute('x-on:click') || '';
+        const isCurrent = expr.indexOf("activeTab = '" + tab + "'") !== -1;
+        if (isCurrent) {
+            btn.setAttribute('aria-current', 'page');
+        } else {
+            btn.removeAttribute('aria-current');
+        }
+    });
+};
+
+// Escape closes the mobile nav drawer and returns focus to the hamburger;
+// opening the drawer moves focus to its first tab.
+(function() {
+    function appData() {
+        const el = document.querySelector('[x-data]');
+        return el && el._x_dataStack && el._x_dataStack[0];
+    }
+    document.addEventListener('keydown', function(e) {
+        if (e.key !== 'Escape') return;
+        const data = appData();
+        if (data && data.mobileNavOpen) {
+            data.mobileNavOpen = false;
+            const burger = document.querySelector('[aria-controls="site-nav"]');
+            if (burger) burger.focus();
+        }
+    });
+    document.addEventListener('click', function(e) {
+        const burger = e.target && e.target.closest
+            ? e.target.closest('[aria-controls="site-nav"]') : null;
+        if (!burger) return;
+        // The click handler toggles mobileNavOpen; focus the first tab once
+        // the drawer has slid in (matches the CSS transition timing).
+        setTimeout(function() {
+            const data = appData();
+            if (data && data.mobileNavOpen) {
+                const first = document.querySelector('#site-nav .nav-tab');
+                if (first) first.focus();
+            }
+        }, 120);
+    });
+})();
+
 // ===== Mobile nav: header-widget relocation =====
 // Below the md breakpoint the settings-search box and system-stats block are
 // MOVED (same DOM nodes, listeners intact) from the header into the nav

web_interface/static/v3/js/app-shell.js

@@ -312,15 +312,29 @@
                         if (typeof this.updatePluginTabStates === 'function') {
                             this.updatePluginTabStates();
                         }
+                        // Screen readers announce the current tab (covers every
+                        // path that changes tabs: clicks, search deep links,
+                        // the getting-started checklist)
+                        if (typeof window.updateNavAriaCurrent === 'function') {
+                            window.updateNavAriaCurrent(newTab);
+                        }
+                        // Floating preview hides on Overview (full preview
+                        // there), reappears per its saved state elsewhere
+                        if (typeof window.updateFloatingPreviewVisibility === 'function') {
+                            window.updateFloatingPreviewVisibility(newTab);
+                        }
                         // Trigger content load when tab changes
                         this.$nextTick(() => {
                             this.loadTabContent(newTab);
                         });
                     });
-                    
+
                     // Load initial tab content
                     this.$nextTick(() => {
                         this.loadTabContent(this.activeTab);
+                        if (typeof window.updateNavAriaCurrent === 'function') {
+                            window.updateNavAriaCurrent(this.activeTab);
+                        }
                     });
 
                     // Listen for plugin updates from pluginManager
@@ -1860,7 +1874,15 @@
             const canvas = document.getElementById('gridOverlay');
             const ledCanvas = document.getElementById('ledCanvas');
             const placeholder = document.getElementById('displayPlaceholder');
-            
+
+            // Feed the floating mini preview (lives in base.html, present on
+            // every tab) before the overview-only guard below.
+            const floatImg = document.getElementById('floating-preview-img');
+            const floatPanel = document.getElementById('floating-preview');
+            if (floatImg && floatPanel && floatPanel.style.display !== 'none' && data.image) {
+                floatImg.src = `data:image/png;base64,${data.image}`;
+            }
+
             if (!stage || !img || !placeholder) return; // Not on overview page
 
             if (data.image) {

web_interface/templates/v3/base.html

@@ -555,6 +555,27 @@
         </nav>
         </div> <!-- /#site-nav -->
 
+        <!-- Floating mini display preview: available on every tab except
+             Overview (which has the full preview). Fed from the same SSE
+             stream by updateDisplayPreview in app-shell.js; open/closed state
+             persists in localStorage. -->
+        <div id="floating-preview" class="floating-preview" style="display:none">
+            <div class="flex items-center justify-between px-2 py-1">
+                <span class="text-xs text-gray-300"><i class="fas fa-tv mr-1"></i>Live Preview</span>
+                <button type="button" onclick="window.toggleFloatingPreview(false)"
+                        class="text-gray-400 hover:text-white ml-2" aria-label="Close live preview">
+                    <i class="fas fa-times text-xs"></i>
+                </button>
+            </div>
+            <img id="floating-preview-img" alt="Live display preview"
+                 style="image-rendering: pixelated; display: block; width: 256px; height: auto;">
+        </div>
+        <button id="floating-preview-toggle" type="button" onclick="window.toggleFloatingPreview(true)"
+                class="floating-preview-toggle" style="display:none"
+                title="Show live display preview" aria-label="Show live display preview">
+            <i class="fas fa-tv"></i>
+        </button>
+
 
         <!-- Tab content -->
         <div id="tab-content" class="space-y-6">

web_interface/templates/v3/partials/plugin_config.html

@@ -893,6 +893,12 @@
                 <p class="mt-1 text-sm text-gray-600">{{ plugin.description or 'Plugin configuration' }}</p>
             </div>
             <div class="flex items-center space-x-4">
+                <button type="button"
+                        onclick="window.previewPluginNow('{{ plugin.id }}')"
+                        class="btn bg-blue-600 hover:bg-blue-700 text-white px-3 py-1.5 text-sm rounded-md"
+                        title="Run this plugin on the display for 60 seconds and open the live preview">
+                    <i class="fas fa-play mr-1"></i>Preview on display
+                </button>
                 <label class="flex items-center cursor-pointer">
                     <input type="checkbox"
                            id="plugin-enabled-{{ plugin.id }}"