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

tests/test_indexer.py

@@ -1,9 +1,7 @@
 # tests/test_indexer.py — Tests for the indexer module
 import os
-import tempfile
 from pathlib import Path
 
-import pytest
 
 from backend.indexer import (
     _extract_tags,
@@ -14,7 +12,6 @@ from backend.indexer import (
     get_vault_names,
     get_vault_data,
     get_backlinks,
-    get_conflicts,
     SUPPORTED_EXTENSIONS,
     _scan_vault,
     load_vault_config,