fix: resolve 48 lint errors in test files

- Remove whitespace from 22 blank lines (W293)
- Remove 6 unused imports (F401): os, Mock, MagicMock, Path
- Add missing imports for 12 test functions (F821): sanitize_filename, extract_remote_path, MagicMock
- Fix 1 unsorted import block (I001)

All ruff checks now pass successfully.

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

tests/test_diagnostic.py

@@ -1,6 +1,6 @@
 """Tests for app/api/diagnostic.py module."""
 
-from unittest.mock import MagicMock, patch
+from unittest.mock import patch
 
 import pytest