fix: resolve 57 ruff lint errors (unused imports, unused variables, import placement)

tests/test_watcher.py

@@ -2,6 +2,7 @@
 import asyncio
 import os
 from pathlib import Path
+import tempfile
 from unittest.mock import MagicMock, patch, AsyncMock
 
 import pytest
@@ -140,7 +141,8 @@ class TestVaultWatcher:
 class TestOnVaultChange:
     @pytest.fixture
     def setup_vault(self):
-        import tempfile, shutil
+        import tempfile
+        import shutil
         from pathlib import Path
         from backend.indexer import build_index, index
         import asyncio
@@ -181,6 +183,3 @@ class TestOnVaultChange:
         }]
         asyncio.run(_on_vault_change(events))
         # Should not crash
-
-
-import tempfile