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/blueprints/api_v3/config.py

@@ -1014,7 +1014,7 @@ def save_main_config():
         plugin_manifests = _pkg._discovered_plugin_manifests()
         for key in data:
             # Check if this key is a plugin ID
-            if api_v3.plugin_manager and key in plugin_manifests:
+            if api_v3.plugin_catalog and key in plugin_manifests:
                 plugin_id = key
                 submitted_config = data[key]
                 if not isinstance(submitted_config, dict):
@@ -1030,7 +1030,7 @@ def save_main_config():
                 # the schema load are far enough apart that a later edit could
                 # separate them. Refuse rather than save without knowing which
                 # fields are secrets.
-                schema_path = resolve_under(api_v3.plugin_manager.plugins_dir,
+                schema_path = resolve_under(api_v3.plugin_catalog.plugins_dir,
                                             plugin_id, 'config_schema.json')
                 if schema_path is None:
                     return error_response(
@@ -1116,18 +1116,9 @@ def save_main_config():
 
         invalidate_cache()
 
-        # Notify saved plugins of their new config (with secrets merged), now
-        # that it is on disk.
-        for plugin_id in plugin_keys_to_remove:
-            try:
-                plugin_instance = api_v3.plugin_manager.get_plugin(plugin_id)
-                if plugin_instance and hasattr(plugin_instance, 'on_config_change'):
-                    merged_config = api_v3.config_manager.load_config()
-                    plugin_instance.on_config_change(_pkg._prepared_plugin_config(
-                        plugin_id, merged_config.get(plugin_id, {})))
-            except Exception as hook_err:
-                # Don't fail the save if hook fails
-                logger.warning("on_config_change failed: %s", hook_err)
+        # Saved plugin sections reach the running plugins through the display
+        # process's config watcher (on_config_change there); nothing runs a
+        # plugin in this process.
 
         message = 'Configuration saved successfully'
         # Switching automatic updates on finishes their setup, which needs
@@ -1139,7 +1130,10 @@ def save_main_config():
                 message = f'{message}. {note}'
         except Exception:
             logger.warning("Automatic update setup could not be started", exc_info=True)
-        return success_response(message=message)
+        # Display hardware, rotation/durations and general settings take
+        # effect after a display restart; the UI shows its restart banner on
+        # this flag.
+        return success_response(message=message, extra={'restart_required': True})
     except Exception as e:
         logger.error("Error saving config", exc_info=True)
         return error_response(