fix(tests): restore pytest import and update package-lock.json

Backend:
- Restore pytest import in test_file_security.py (needed for pytest.raises)

Frontend:
- Update package-lock.json with @vitest/coverage-v8 dependencies
- Resolves npm ci error in CI workflows

This completes all CI fixes for linting and dependency issues.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: zhijiewong

backend/tests/unit/test_file_security.py

@@ -1,4 +1,5 @@
 """Unit tests for file security utilities."""
+import pytest
 from app.utils.file_security import (
     sanitize_filename,
     validate_file_extension,