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>

test/web_interface/test_update_all_plugins.py

@@ -41,7 +41,7 @@ def store(tmp_path):
     sm.get_plugin_info.return_value = None
     sm.update_plugin.return_value = True
     with patch.object(api_v3, 'plugin_store_manager', sm, create=True), \
-         patch.object(api_v3, 'plugin_manager', None, create=True), \
+         patch.object(api_v3, 'plugin_catalog', None, create=True), \
          patch.object(api_v3, 'schema_manager', None, create=True), \
          patch.object(api_v3, 'plugin_state_manager', None, create=True), \
          patch.object(api_v3, 'operation_history', None, create=True):