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_style_editor_extra_fields.py

@@ -64,7 +64,7 @@ def post(tmp_path):
     from web_interface.blueprints import api_v3 as a
 
     originals = {k: getattr(a.api_v3, k, None)
-                 for k in ("config_manager", "schema_manager", "plugin_manager")}
+                 for k in ("config_manager", "schema_manager", "plugin_catalog")}
 
     pdir = tmp_path / "plugins" / "demo"
     pdir.mkdir(parents=True)
@@ -86,9 +86,7 @@ def post(tmp_path):
     a.api_v3.schema_manager = SchemaManager(plugins_dir=tmp_path / "plugins",
                                             project_root=tmp_path)
     pm = MagicMock()
-    pm.plugins = {}
-    pm.get_plugin.return_value = None
-    a.api_v3.plugin_manager = pm
+    a.api_v3.plugin_catalog = pm
 
     app = Flask(__name__)
     app.config["TESTING"] = True