feat(web): add update-available banner to web UI

Adds a polite, dismissible banner between the header and navigation
tabs that appears when the local repo is behind origin/main. Shows
commit count and a one-click "Update Now" button that triggers the
existing git_pull action.

- New GET /api/v3/system/check-update endpoint (5-min cache, compares
  local HEAD vs origin/main SHA)
- Banner auto-checks on page load then every 30 minutes
- Dismiss persists for the browser session via sessionStorage
- Styled for both light and dark themes
- Cache invalidated after successful git_pull so banner hides immediately

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

web_interface/blueprints/api_v3.py

@@ -1341,6 +1341,57 @@ def get_system_version():
         logger.exception("[System] get_system_version failed")
         return jsonify({'status': 'error', 'message': 'Failed to get system version'}), 500
 
+_update_check_cache: Dict = {}
+_UPDATE_CHECK_TTL = 300  # 5 minutes
+
+@api_v3.route('/system/check-update', methods=['GET'])
+def check_for_update():
+    """Check if a newer version is available on the remote."""
+    import time as _time
+    now = _time.time()
+    if _update_check_cache.get('ts', 0) + _UPDATE_CHECK_TTL > now:
+        return jsonify(_update_check_cache['data'])
+
+    project_dir = str(PROJECT_ROOT)
+    try:
+        subprocess.run(
+            ['git', 'fetch', 'origin', 'main'],
+            capture_output=True, text=True, timeout=15, cwd=project_dir
+        )
+        local_sha = subprocess.run(
+            ['git', 'rev-parse', 'HEAD'],
+            capture_output=True, text=True, timeout=5, cwd=project_dir
+        ).stdout.strip()
+        remote_sha = subprocess.run(
+            ['git', 'rev-parse', 'origin/main'],
+            capture_output=True, text=True, timeout=5, cwd=project_dir
+        ).stdout.strip()
+
+        if local_sha == remote_sha:
+            data = {'status': 'success', 'update_available': False,
+                    'local_sha': local_sha[:8], 'remote_sha': remote_sha[:8]}
+        else:
+            log_result = subprocess.run(
+                ['git', 'log', 'HEAD..origin/main', '--oneline'],
+                capture_output=True, text=True, timeout=5, cwd=project_dir
+            )
+            lines = [l for l in log_result.stdout.strip().split('\n') if l]
+            data = {
+                'status': 'success',
+                'update_available': True,
+                'local_sha': local_sha[:8],
+                'remote_sha': remote_sha[:8],
+                'commits_behind': len(lines),
+                'latest_message': lines[0].split(' ', 1)[1] if lines else '',
+            }
+    except Exception as e:
+        logger.warning("[System] check-update failed: %s", e)
+        data = {'status': 'error', 'update_available': False, 'message': str(e)}
+
+    _update_check_cache['ts'] = now
+    _update_check_cache['data'] = data
+    return jsonify(data)
+
 @api_v3.route('/system/action', methods=['POST'])
 def execute_system_action():
     """Execute system actions (start/stop/reboot/etc)"""
@@ -1450,6 +1501,9 @@ def execute_system_action():
                 cwd=project_dir
             )
 
+            # Invalidate update-check cache so the banner hides immediately
+            _update_check_cache.clear()
+
             # Return custom response for git_pull
             if result.returncode == 0:
                 pull_message = "Code updated successfully."

web_interface/static/v3/app.css

@@ -1004,3 +1004,39 @@ button.bg-white {
 [data-theme="dark"] .theme-toggle-btn {
     color: #fbbf24;
 }
+
+/* Update available banner */
+.update-banner {
+    background-color: #eff6ff;
+    border-color: #bfdbfe;
+    color: #1e40af;
+}
+.update-banner-action {
+    background-color: #3b82f6;
+    color: #fff;
+}
+.update-banner-action:hover {
+    background-color: #2563eb;
+}
+.update-banner-dismiss {
+    color: #1e40af;
+    opacity: 0.6;
+}
+.update-banner-dismiss:hover {
+    opacity: 1;
+}
+
+[data-theme="dark"] .update-banner {
+    background-color: #1e293b;
+    border-color: #334155;
+    color: #93c5fd;
+}
+[data-theme="dark"] .update-banner-action {
+    background-color: #2563eb;
+}
+[data-theme="dark"] .update-banner-action:hover {
+    background-color: #3b82f6;
+}
+[data-theme="dark"] .update-banner-dismiss {
+    color: #93c5fd;
+}

web_interface/templates/v3/base.html

@@ -931,6 +931,33 @@
         </div>
     </header>
 
+    <!-- Update available banner -->
+    <div id="update-banner" style="display:none"
+         class="update-banner border-b transition-all duration-300 ease-in-out">
+        <div class="mx-auto px-4 sm:px-6 lg:px-8 xl:px-12 2xl:px-16 py-2" style="max-width:100%">
+            <div class="flex items-center justify-between">
+                <div class="flex items-center space-x-3">
+                    <i class="fas fa-arrow-circle-up text-lg"></i>
+                    <span class="text-sm font-medium" id="update-banner-text">
+                        A new LEDMatrix update is available
+                    </span>
+                </div>
+                <div class="flex items-center space-x-3">
+                    <button onclick="applyUpdate()" id="update-banner-btn"
+                            class="inline-flex items-center px-3 py-1 text-xs font-semibold rounded-md
+                                   update-banner-action transition-colors duration-150">
+                        <i class="fas fa-download mr-1"></i> Update Now
+                    </button>
+                    <button onclick="dismissUpdateBanner()"
+                            class="update-banner-dismiss rounded p-1 transition-colors duration-150"
+                            title="Dismiss">
+                        <i class="fas fa-times text-sm"></i>
+                    </button>
+                </div>
+            </div>
+        </div>
+    </div>
+
     <!-- Main content -->
     <main class="mx-auto px-4 sm:px-6 lg:px-8 xl:px-12 2xl:px-16 py-8" style="max-width: 100%;">
         <!-- Navigation tabs -->
@@ -4888,6 +4915,72 @@
             </form>
         </div>
     </div>
+<!-- Update banner logic -->
+<script>
+(function() {
+    var CHECK_INTERVAL = 30 * 60 * 1000; // 30 minutes
+    var _dismissed = false;
+
+    function checkForUpdate() {
+        fetch('/api/v3/system/check-update')
+            .then(function(r) { return r.json(); })
+            .then(function(data) {
+                if (data.update_available && !_dismissed) {
+                    var n = data.commits_behind || 0;
+                    var msg = 'A new LEDMatrix update is available';
+                    if (n > 0) msg += ' (' + n + ' commit' + (n > 1 ? 's' : '') + ')';
+                    document.getElementById('update-banner-text').textContent = msg;
+                    document.getElementById('update-banner').style.display = '';
+                    try { sessionStorage.setItem('update-sha', data.remote_sha); } catch(e) {}
+                } else {
+                    document.getElementById('update-banner').style.display = 'none';
+                }
+            })
+            .catch(function() {});
+    }
+
+    window.dismissUpdateBanner = function() {
+        _dismissed = true;
+        document.getElementById('update-banner').style.display = 'none';
+        try { sessionStorage.setItem('update-dismissed', '1'); } catch(e) {}
+    };
+
+    window.applyUpdate = function() {
+        var btn = document.getElementById('update-banner-btn');
+        btn.innerHTML = '<i class="fas fa-spinner fa-spin mr-1"></i> Updating...';
+        btn.disabled = true;
+        fetch('/api/v3/system/action', {
+            method: 'POST',
+            headers: { 'Content-Type': 'application/json' },
+            body: JSON.stringify({ action: 'git_pull' })
+        })
+        .then(function(r) { return r.json(); })
+        .then(function(data) {
+            document.getElementById('update-banner').style.display = 'none';
+            if (typeof showNotification === 'function') {
+                showNotification(data.message || 'Update complete', data.status || 'success');
+            }
+            try { sessionStorage.removeItem('update-dismissed'); } catch(e) {}
+        })
+        .catch(function() {
+            btn.innerHTML = '<i class="fas fa-download mr-1"></i> Update Now';
+            btn.disabled = false;
+            if (typeof showNotification === 'function') {
+                showNotification('Update failed — check your connection', 'error');
+            }
+        });
+    };
+
+    // On load: skip if dismissed this session for the same SHA
+    try {
+        if (sessionStorage.getItem('update-dismissed') === '1') _dismissed = true;
+    } catch(e) {}
+
+    // Initial check shortly after page load, then periodic
+    setTimeout(checkForUpdate, 2000);
+    setInterval(checkForUpdate, CHECK_INTERVAL);
+})();
+</script>
 </body>
 </html>