fix(ruff): #61 I001 import sorting + RUF012 ClassVar annotation

backend/plugins.py

@@ -9,10 +9,11 @@ enable / disable), all scoped to a single vault.
 import json
 import logging
 import re
+import time as _time
 import zipfile
 from dataclasses import dataclass, field
 from pathlib import Path
-from typing import Any
+from typing import Any, ClassVar
 
 from fastapi import APIRouter, Depends, File, HTTPException, UploadFile
 from fastapi.responses import JSONResponse
@@ -560,11 +561,11 @@ async def api_disable_plugin(vault: str, plugin_name: str, current_user=Depends(
 # ── Plugin Event Bus ────────────────────────────────────────────────────────
 # Lightweight pub/sub for backend events that plugins can subscribe to.
 # Used to dispatch onFileCreate, onFileDelete, onVaultMount to enabled plugins.
-import time as _time
+
 
 class _PluginEventBus:
     """In-memory event dispatcher for plugin lifecycle events."""
-    _listeners: dict[str, list] = {}
+    _listeners: ClassVar[dict[str, list]] = {}
 
     @classmethod
     def subscribe(cls, event_type: str, callback) -> None: