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/integration/test_totp.py

@@ -1,7 +1,7 @@
 """
 Integration tests for TOTP 2FA operations.
 """
-import pytest
+
 import pyotp
 
 
@@ -38,9 +38,7 @@ class TestTOTPSetup:
 
         # Verify the code
         response = test_app.post(
-            "/api/auth/setup-2fa/verify",
-            headers=admin_headers,
-            json={"secret": secret, "code": valid_code}
+            "/api/auth/setup-2fa/verify", headers=admin_headers, json={"secret": secret, "code": valid_code}
         )
 
         assert response.status_code == 200
@@ -51,9 +49,7 @@ class TestTOTPSetup:
     def test_verify_2fa_setup_invalid_code(self, test_app, admin_headers):
         """Test verifying 2FA with invalid code."""
         response = test_app.post(
-            "/api/auth/setup-2fa/verify",
-            headers=admin_headers,
-            json={"secret": "JBSWY3DPEHPK3PXP", "code": "000000"}
+            "/api/auth/setup-2fa/verify", headers=admin_headers, json={"secret": "JBSWY3DPEHPK3PXP", "code": "000000"}
         )
 
         assert response.status_code == 400
@@ -63,10 +59,7 @@ class TestTOTPSetup:
 
     def test_verify_2fa_without_auth(self, test_app):
         """Test verifying 2FA without authentication."""
-        response = test_app.post(
-            "/api/auth/setup-2fa/verify",
-            json={"secret": "JBSWY3DPEHPK3PXP", "code": "123456"}
-        )
+        response = test_app.post("/api/auth/setup-2fa/verify", json={"secret": "JBSWY3DPEHPK3PXP", "code": "123456"})
 
         assert response.status_code == 401
 
@@ -100,14 +93,13 @@ class TestTOTPWorkflow:
         totp = pyotp.TOTP(secret)
         valid_code = totp.now()
         verify_response = test_app.post(
-            "/api/auth/setup-2fa/verify",
-            headers=admin_headers,
-            json={"secret": secret, "code": valid_code}
+            "/api/auth/setup-2fa/verify", headers=admin_headers, json={"secret": secret, "code": valid_code}
         )
         assert verify_response.status_code == 200
 
         # Step 3: Verify 2FA is enabled by checking auth_service
         from auth_service import load_totp_secret
+
         saved_secret = load_totp_secret()
         assert saved_secret == secret