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/unit/test_auth.py

@@ -1,30 +1,33 @@
 """
 Unit tests for auth.py - JWT, TOTP, password hashing, encryption.
 """
-import pytest
+
+from datetime import UTC, datetime, timedelta
+
 import jwt
 import pyotp
-from datetime import datetime, timedelta, timezone
+import pytest
+from fastapi import HTTPException
+
 from auth_service import (
-    verify_password,
-    get_password_hash,
+    _decrypt,
+    _encrypt,
+    clear_passkey_credentials,
     create_access_token,
     create_refresh_token,
-    user_from_access_token,
-    verify_totp,
-    load_totp_secret,
-    save_totp_secret,
-    load_password_hash,
-    save_password_hash,
+    get_password_hash,
     increment_token_version,
-    verify_token_version,
-    _encrypt,
-    _decrypt,
     load_passkey_credentials,
+    load_password_hash,
+    load_totp_secret,
     save_passkey_credential,
-    clear_passkey_credentials,
+    save_password_hash,
+    save_totp_secret,
+    user_from_access_token,
+    verify_password,
+    verify_token_version,
+    verify_totp,
 )
-from fastapi import HTTPException
 
 
 class TestPasswordHashing:
@@ -79,8 +82,8 @@ class TestJWTTokens:
         token = create_access_token(data, expires_delta)
 
         payload = jwt.decode(token, mock_config.SECRET_KEY, algorithms=[mock_config.ALGORITHM])
-        exp_time = datetime.fromtimestamp(payload["exp"], tz=timezone.utc)
-        now = datetime.now(timezone.utc)
+        exp_time = datetime.fromtimestamp(payload["exp"], tz=UTC)
+        now = datetime.now(UTC)
 
         # Should expire in approximately 60 minutes
         time_diff = (exp_time - now).total_seconds()
@@ -111,10 +114,7 @@ class TestJWTTokens:
 
     def test_user_from_expired_token(self, mock_config, temp_rbac_file):
         """Test that expired token raises HTTPException."""
-        token = create_access_token(
-            {"sub": "testuser", "role": "admin"},
-            expires_delta=timedelta(seconds=-1)
-        )
+        token = create_access_token({"sub": "testuser", "role": "admin"}, expires_delta=timedelta(seconds=-1))
 
         with pytest.raises(HTTPException) as exc_info:
             user_from_access_token(token)
@@ -141,9 +141,9 @@ class TestJWTTokens:
         """Test that token without username fails."""
         # Create token without 'sub' field
         token = jwt.encode(
-            {"role": "admin", "type": "access", "exp": datetime.now(timezone.utc) + timedelta(minutes=30)},
+            {"role": "admin", "type": "access", "exp": datetime.now(UTC) + timedelta(minutes=30)},
             mock_config.SECRET_KEY,
-            algorithm=mock_config.ALGORITHM
+            algorithm=mock_config.ALGORITHM,
         )
 
         with pytest.raises(HTTPException) as exc_info:
@@ -209,7 +209,9 @@ class TestTOTP:
 
         monkeypatch.setenv("TOTP_SECRET", "ENV_SECRET_KEY")
         import importlib
+
         import config
+
         importlib.reload(config)
 
         # When no secret in file, should return env var
@@ -237,7 +239,9 @@ class TestTOTP:
         # Also clear environment variable fallback
         monkeypatch.setenv("TOTP_SECRET", "")
         import importlib
+
         import config
+
         importlib.reload(config)
         # No secret saved, should return True (2FA disabled)
         assert verify_totp("any_code")
@@ -248,10 +252,11 @@ class TestTOTP:
 
         # Ensure auth file is properly initialized with last_totp_ts
         import json
-        with open(temp_auth_file, 'r') as f:
+
+        with open(temp_auth_file) as f:
             data = json.load(f)
-        data['last_totp_ts'] = 0
-        with open(temp_auth_file, 'w') as f:
+        data["last_totp_ts"] = 0
+        with open(temp_auth_file, "w") as f:
             json.dump(data, f)
 
         totp = pyotp.TOTP(sample_totp_secret)
@@ -280,15 +285,18 @@ class TestPasswordPersistence:
         """Test loading password hash from environment variable."""
         # Clear any hash in the file first
         import json
-        with open(temp_auth_file, 'r') as f:
+
+        with open(temp_auth_file) as f:
             data = json.load(f)
-        data['password_hash'] = ""
-        with open(temp_auth_file, 'w') as f:
+        data["password_hash"] = ""
+        with open(temp_auth_file, "w") as f:
             json.dump(data, f)
 
         # Reload auth_service to clear any cached data
-        import auth_service
         import importlib
+
+        import auth_service
+
         importlib.reload(auth_service)
 
         # When no hash in file, should return env var