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/plugin_store.py

@@ -8,7 +8,7 @@ from web_interface.blueprints.api_v3 import (
     ErrorCode, OperationType, Path, _do_transactional_uninstall,
     _non_plugin_id_error, _get_plugin_version, _plugin_directory,
     _plugin_enabled_in_config, _store_restart_fields, api_v3,
-    datetime, error_response, exception_error_response, json, jsonify, logger,
+    error_response, exception_error_response, json, jsonify, logger,
     request, success_response, validate_request_json,
 )
 from src.common.path_safety import resolve_under, safe_path_component
@@ -236,12 +236,8 @@ def update_plugin():
             if api_v3.plugin_catalog:
                 api_v3.plugin_catalog.discover_plugins()
 
-            # Update state and history
-            if api_v3.plugin_state_manager:
-                api_v3.plugin_state_manager.update_plugin_state(
-                    plugin_id,
-                    {'last_updated': datetime.now()}
-                )
+            # Record in history (the only record of when it was updated;
+            # the version is the manifest on disk).
             if api_v3.operation_history:
                 version = _get_plugin_version(plugin_id)
                 api_v3.operation_history.record_operation(
@@ -467,10 +463,6 @@ def install_plugin():
                 if api_v3.plugin_catalog:
                     api_v3.plugin_catalog.discover_plugins()
 
-                # Update state manager
-                if api_v3.plugin_state_manager:
-                    api_v3.plugin_state_manager.set_plugin_installed(plugin_id)
-
                 # Record in history
                 if api_v3.operation_history:
                     version = _get_plugin_version(plugin_id)
@@ -529,8 +521,6 @@ def install_plugin():
                 api_v3.schema_manager.invalidate_cache(plugin_id)
             if api_v3.plugin_catalog:
                 api_v3.plugin_catalog.discover_plugins()
-            if api_v3.plugin_state_manager:
-                api_v3.plugin_state_manager.set_plugin_installed(plugin_id)
             if api_v3.operation_history:
                 version = _get_plugin_version(plugin_id)
                 api_v3.operation_history.record_operation(