feat: comprehensive test infrastructure improvements

- Fix unit test imports: add env setup in conftest.py before module imports
- Add 24 new auth router tests (RBAC, preferences, password validation)
- Add 16 new tests for litellm and chat_summary routers
- Apply black formatting and ruff linting across codebase
- Add pre-commit hooks configuration (black, ruff, file checks)
- Increase CI coverage threshold from 40% to 50%

Test Results:
- 206 tests passing (91 unit + 115 integration)
- Coverage: 58.79% on core modules
- auth.py: 57% → 85%, litellm.py: 23% → 87%, chat_summary.py: 41% → 100%
- auth_service: 96.51%, config: 100%, rbac: 93.48%

dashboard/backend/tests/test_basic.py

@@ -1,8 +1,8 @@
 """
 Basic diagnostic tests to validate test environment.
 """
+
 import sys
-import pytest
 
 
 def test_python_version():
@@ -13,18 +13,19 @@ def test_python_version():
 def test_imports():
     """Verify all required modules can be imported."""
     try:
-        import fastapi
-        import uvicorn
+        import asyncssh
         import docker
+        import fastapi
         import httpx
         import jwt
         import passlib
         import pyotp
-        import asyncssh
         import pytest
         import pytest_asyncio
         import pytest_cov
         import pytest_mock
+        import uvicorn
+
         assert True
     except ImportError as e:
         pytest.fail(f"Import failed: {e}")