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_plugin_config_schema_expansion.py

@@ -71,7 +71,7 @@ def render(tmp_path):
     from web_interface.blueprints import pages_v3 as pv
     from src.plugin_system.schema_manager import SchemaManager
 
-    orig_pm = getattr(pv.pages_v3, "plugin_manager", None)
+    orig_pm = getattr(pv.pages_v3, "plugin_catalog", None)
     orig_cm = getattr(pv.pages_v3, "config_manager", None)
     orig_sm = getattr(pv.pages_v3, "schema_manager", None)
 
@@ -86,8 +86,7 @@ def render(tmp_path):
         pm = MagicMock()
         pm.plugins_dir = str(tmp_path / "plugins")
         pm.get_plugin_info.return_value = {"id": plugin_id, "name": plugin_id}
-        pm.get_plugin.return_value = None
-        pv.pages_v3.plugin_manager = pm
+        pv.pages_v3.plugin_catalog = pm
 
         cm = MagicMock()
         cm.load_config.return_value = {plugin_id: {"enabled": True}}
@@ -111,7 +110,7 @@ def render(tmp_path):
     try:
         yield _render
     finally:
-        pv.pages_v3.plugin_manager = orig_pm
+        pv.pages_v3.plugin_catalog = orig_pm
         pv.pages_v3.config_manager = orig_cm
         pv.pages_v3.schema_manager = orig_sm