refactor(web): read plugins through a PluginCatalog; only the display runs them (#688)

The web process built its own PluginManager and loaded plugins into itself:
store installs and updates loaded or reloaded a web-side copy, and config
saves and enable/disable called on_config_change, on_enable and on_disable
on it. None of that reached the panel, and /plugins/installed reported
runtime state from those copies.

- Add PluginCatalog (src/plugin_system/plugin_catalog.py): manifests,
  directories, display modes, installed version, schema and config reads,
  with no way to run a plugin. app.py and both blueprints use it; the
  plugin_manager blueprint attribute is gone.
- Remove every lifecycle call from the web routes. Config changes already
  reach the display through ConfigService (on_config_change) and the
  enabled-set reconcile.
- Health and metrics readers move to api_v3.health_tracker /
  resource_monitor. /plugins/installed reports loaded/state/error_info as
  null (the display does not publish them) and enabled by the display's
  rule.
- Store install, update and uninstall answer restart_required when the
  running display will not pick the change up by itself
  (display_restart_required). The restart banner follows the flag via
  window.noteRestartRequired instead of the /config/main URL heuristic;
  /config/main now sends restart_required: true.
- The one remaining in-process import of plugin code (Starlark helper
  modules, oauth_flow action scripts) goes through
  _import_plugin_code_in_web_process() until a web-entry contract.
- /plugins/installed reports vegas_participation (from #682) from the
  user's setting or the manifest, with vegas_participation_source; when
  only the plugin's code decides it, null with source 'runtime', since the
  web process no longer has plugin instances to ask.
- Check & Update All keeps its restart flags when the final list refresh
  fails, and asks for a restart when an enabled plugin's first request got
  no answer and the re-sent one found it up to date.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web_interface/static/v3/app.js

@@ -27,8 +27,9 @@
  * the display" banner; the floating live preview; aria-current on the nav;
  * the mobile nav drawer's keyboard handling; header widget placement.
  *
- * Globals: showSaveResult, showRestartPending, dismissRestartPending,
- * restartPendingNow, toggleFloatingPreview, applyFloatingPreviewSize,
+ * Globals: showSaveResult, showRestartPending, noteRestartRequired,
+ * dismissRestartPending, restartPendingNow, toggleFloatingPreview,
+ * applyFloatingPreviewSize,
  * cycleFloatingPreviewSize, updateFloatingPreviewVisibility,
  * previewPluginNow, updateNavAriaCurrent, placeHeaderWidgets.
  */
@@ -72,19 +73,31 @@ document.body.addEventListener('htmx:afterRequest', function(event) {
         }
     }
 
-    // Main-config saves (display hardware, rotation/durations, general) only
-    // take effect after a display-service restart — surface the reminder
-    // banner. Plugin config saves apply live and are deliberately excluded.
+    // A response that needs a display restart to take effect says so with
+    // restart_required (main-config saves, store operations the display
+    // cannot pick up live); surface the reminder banner for it.
     try {
-        const cfg = event.detail.requestConfig;
-        if (cfg && cfg.verb === 'post' &&
-            (cfg.path || '').includes('/api/v3/config/main') &&
-            response && response.status >= 200 && response.status < 300) {
-            window.showRestartPending();
+        if (response && response.status >= 200 && response.status < 300 && response.responseText) {
+            window.noteRestartRequired(JSON.parse(response.responseText));
         }
-    } catch { /* banner is best-effort */ }
+    } catch { /* not JSON; the banner is best-effort */ }
 });
 
+/**
+ * Shows the restart-pending banner when an API response says the change
+ * needs a display restart (`restart_required: true`), with the response's
+ * `restart_message` as its wording when there is one. Every caller of an
+ * endpoint that can answer this way passes the parsed body here, so the
+ * server alone decides when the banner appears.
+ * @param {Object} data - a parsed JSON response body (or an operation result)
+ * @returns {boolean} whether the banner was shown
+ */
+window.noteRestartRequired = function(data) {
+    if (!data || data.restart_required !== true) return false;
+    window.showRestartPending(typeof data.restart_message === 'string' ? data.restart_message : undefined);
+    return true;
+};
+
 /**
  * Shows the outcome of a settings form save as one notification. Used by the
  * hx-on:htmx:after-request of the Display, Rotation & Durations and General