refactor(plugins): the display publishes plugin runtime state; retire plugin_state.json (#690)

Stage 2 of the web plugin catalog, after #688.

- The display publishes a plugin runtime snapshot (plugin_runtime.py) to
  the shared cache: per plugin loaded, lifecycle state, a short redacted
  error summary, the version it loaded and when, plus published_at /
  stale_after / running. Written on change (throttled to 10 s; the
  RUNNING/ENABLED flip of an ordinary update is not a change) and once a
  minute otherwise; cleanup() publishes running: false.
- The web reads it back and restores loaded / state / error_info in
  /api/v3/plugins/installed (plus loaded_version, loaded_at and
  data.runtime). Only a live snapshot counts; stale, stopped or missing
  answers null and says which.
- data/plugin_state.json is retired: every reader and writer moved to
  config + disk (desired) or the snapshot (observed). Nothing in it was
  non-derivable, so nothing is migrated and an existing file is left
  unread. The web-side PluginStateManager (state_manager.py) is removed;
  the display's plugin_state.PluginStateManager is the only state machine.
- StateReconciliation compares config + disk with the snapshot, reporting
  enabled-but-not-loaded and older-version-loaded as no_action findings.
- Backups list installed manifests with enabled from config.json.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

web_interface/blueprints/api_v3/__init__.py

@@ -720,8 +720,6 @@ def _do_transactional_uninstall(plugin_id, preserve_config):
     # --- Step 4: finish ---
     if api_v3.schema_manager:
         api_v3.schema_manager.invalidate_cache(plugin_id)
-    if api_v3.plugin_state_manager:
-        api_v3.plugin_state_manager.remove_plugin_state(plugin_id)
     # Persistently record the uninstall so a later core `git pull` update
     # cannot resurrect a built-in plugin (committed under plugin-repos/) that
     # the user removed. Best-effort: never fail the uninstall over this.
@@ -730,6 +728,17 @@ def _do_transactional_uninstall(plugin_id, preserve_config):
     except Exception as record_err:
         logger.warning("Could not record uninstall for %s: %s", plugin_id, record_err)
     return True, None
+def _plugin_runtime_view():
+    """What the display publishes about its plugins (loaded, lifecycle
+    state, last error, version loaded), judged for staleness.
+
+    Only a ``live`` view reports those facts; a stale, stopped or missing
+    snapshot answers None for them (see src/plugin_system/plugin_runtime.py).
+    """
+    from src.plugin_system.plugin_runtime import read_plugin_runtime
+    return read_plugin_runtime(getattr(api_v3, 'cache_manager', None))
+
+
 def _plugin_enabled_in_config(plugin_id: str) -> bool:
     """Whether config.json enables ``plugin_id``, by the display's rule.