fix(web): widget cache-busting, dead frontend code, and dependency pins (#656)

- Plugin-supplied widgets load as /static/plugin-widgets/...js?v=<plugin
  version>, so an update isn't hidden behind the year-long immutable cache.
- Fire-and-forget loadInstalledPlugins() calls catch the rejection it has
  already reported, so the global handler no longer adds a second toast.
- Timezone picker renders again when the General partial is re-injected.
- Remove dead code: executePluginAction's six plugin-id fallbacks and
  [DEBUG] logging, window.currentPluginConfig and every read of it, the
  file-upload JSON delete branch, unused PluginAPI / PluginInstallManager /
  PluginStateManager helpers, loadPluginWidgetsFromManifest, the stale
  install_manager.js and LEDVisibility fallbacks, error_handler.js's global
  escapeHtml, 13 unused CSS rules, and stale comments/no-op returns.
- pytz < 2027, psutil < 7 in requirements-test.txt, pytest-cov < 8.
- Pin anthropics/claude-code-action to the commit v1 resolves to.

Co-authored-by: Claude Opus 5.5 <noreply@anthropic.com>

web_interface/templates/v3/partials/general.html

@@ -88,9 +88,6 @@
         </div>
         <script>
         (function() {
-            // Track if already initialized to prevent re-render
-            if (window.__timezoneWidgetInitialized) return;
-
             function initTimezoneWidget() {
                 if (!window.LEDMatrixWidgets) { setTimeout(initTimezoneWidget, 50); return; }
                 var widget = window.LEDMatrixWidgets.get('timezone-selector');
@@ -107,7 +104,6 @@
                     fieldId: 'timezone',
                     name: 'timezone'
                 });
-                window.__timezoneWidgetInitialized = true;
             }
             if (document.readyState === 'loading') {
                 document.addEventListener('DOMContentLoaded', initTimezoneWidget);