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/plugins_manager.js

@@ -453,6 +453,7 @@ window.handleGitHubPluginInstall = function() {
             urlInput.value = '';
 
             showNotification(`Plugin ${data.plugin_id} installed successfully`, 'success');
+            window.noteRestartRequired(data);
 
             setTimeout(() => window.pluginManager.loadInstalledPlugins(true).catch(() => {}), 1000);
         } else {
@@ -1548,6 +1549,9 @@ function runUpdateAllPlugins() {
             // a no-op update is "already up to date", not "updated".
             const summary = window.PluginInstallManager.summarizeUpdateResults(results);
             showNotification(summary.text, summary.type);
+            // An updated plugin the display is running keeps its old code
+            // until the display restarts.
+            window.noteRestartRequired(window.PluginInstallManager.restartRequest(results));
         })
         .catch(error => {
             console.error('Error updating all plugins:', error);
@@ -2062,6 +2066,7 @@ window.uninstallPlugin = function(pluginId) {
             pollOperationStatus(operationId, pluginId, pluginName);
         } else if (data.status === 'success') {
             // Direct uninstall completed immediately
+            window.noteRestartRequired(data);
             handleUninstallSuccess(pluginId);
         } else {
             // Error response
@@ -2104,6 +2109,9 @@ function pollOperationStatus(operationId, pluginId, pluginName, options = {}) {
                 const status = operation.status;
 
                 if (status === 'completed') {
+                    // The operation's result says whether the display picks
+                    // the change up by itself or needs a restart.
+                    window.noteRestartRequired(operation.result);
                     onComplete();
                 } else if (status === 'failed') {
                     onFailed(operation.error || operation.message);
@@ -2549,6 +2557,7 @@ window.installPlugin = function(pluginId, branch = null) {
             });
         } else {
             // No operation queue configured - install already completed synchronously.
+            window.noteRestartRequired(data);
             enableAfterInstall();
         }
     })
@@ -2579,6 +2588,7 @@ window.installFromCustomRegistry = function(pluginId, registryUrl, pluginPath, b
     .then(data => {
         if (data.status === 'success') {
             showNotification(`Plugin ${data.plugin_id} installed successfully`, 'success');
+            window.noteRestartRequired(data);
             // Refresh installed plugins and re-render custom registry
             loadInstalledPlugins().catch(() => {});
             // Re-render custom registry to update install buttons
@@ -2771,6 +2781,7 @@ function attachInstallButtonHandler() {
                             pluginStatusDiv.innerHTML = `<span class="text-green-600"><i class="fas fa-check-circle mr-1"></i>Successfully installed: ${escapeHtml(data.plugin_id)}</span>`;
                         }
                         pluginUrlInput.value = '';
+                        window.noteRestartRequired(data);
 
                         // Refresh installed plugins list
                         setTimeout(() => {