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/test_web_plugin_dir_resolution.py

@@ -46,8 +46,8 @@ def prefixed_plugin(tmp_path, api_v3_module):
     }), encoding="utf-8")
 
     api = api_v3_module.api_v3
-    api.plugin_manager.plugins_dir = str(plugins_dir)
-    api.plugin_manager.get_plugin_directory = MagicMock(side_effect=_resolver(plugins_dir))
+    api.plugin_catalog.plugins_dir = str(plugins_dir)
+    api.plugin_catalog.get_plugin_directory = MagicMock(side_effect=_resolver(plugins_dir))
     api.plugin_store_manager.plugins_dir = str(plugins_dir)
     return plugin_dir
 
@@ -58,8 +58,7 @@ class TestInstalledList:
         api = api_v3_module.api_v3
         info = {"id": "demo", "name": "Demo", "version": "1.0.0",
                 "description": "stale cached copy", "loaded": False}
-        api.plugin_manager.get_all_plugin_info = MagicMock(return_value=[info])
-        api.plugin_manager.get_plugin = MagicMock(return_value=None)
+        api.plugin_catalog.get_all_plugin_info = MagicMock(return_value=[info])
         api.plugin_store_manager.get_registry_info = MagicMock(return_value=None)
         api.plugin_store_manager._get_local_git_info = MagicMock(return_value=None)
         api.config_manager.load_config = MagicMock(return_value={})
@@ -87,7 +86,6 @@ class TestUpdateRoute:
         api.plugin_store_manager.get_plugin_info = MagicMock(return_value=None)
         api.plugin_store_manager.update_plugin = MagicMock(return_value=True)
         api.plugin_store_manager._get_local_git_info = MagicMock(return_value=None)
-        api.plugin_manager.plugins = {}
         api.schema_manager = None
         api.plugin_state_manager = None
         api.operation_history = None
@@ -121,7 +119,6 @@ class TestUpdateRoute:
         api.plugin_store_manager.get_plugin_info = MagicMock(return_value=None)
         api.plugin_store_manager.update_plugin = MagicMock(return_value=False)
         api.plugin_store_manager._get_local_git_info = MagicMock(return_value=None)
-        api.plugin_manager.plugins = {}
         api.operation_history = None
 
         response = api_v3_client.post("/api/v3/plugins/update", json={"plugin_id": "ghost"})
@@ -140,8 +137,7 @@ def pages(tmp_path, monkeypatch):
     plugins_dir.mkdir()
     plugin_manager = MagicMock()
     plugin_manager.plugins_dir = plugins_dir
-    plugin_manager.get_plugin.return_value = None
-    monkeypatch.setattr(module.pages_v3, "plugin_manager", plugin_manager, raising=False)
+    monkeypatch.setattr(module.pages_v3, "plugin_catalog", plugin_manager, raising=False)
     monkeypatch.setattr(module.pages_v3, "config_manager",
                         MagicMock(load_config=lambda: {}), raising=False)
     monkeypatch.setattr(module.pages_v3, "schema_manager", None, raising=False)