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/routers/totp.py

@@ -1,31 +1,34 @@
 """TOTP (Time-based One-Time Password) 2FA endpoints."""
+
+import pyotp
 from fastapi import APIRouter, Depends, HTTPException
 from pydantic import BaseModel
-import pyotp
+
 import auth_service as auth
 
 router = APIRouter()
 
+
 class Setup2FAResponse(BaseModel):
     secret: str
     uri: str
 
+
 class Verify2FARequest(BaseModel):
     secret: str
     code: str
 
+
 @router.post("/setup-2fa/generate", response_model=Setup2FAResponse)
-async def generate_2fa(current_user = Depends(auth.get_current_user)):
+async def generate_2fa(current_user=Depends(auth.get_current_user)):
     """Generate a new TOTP secret and provisioning URI for 2FA setup."""
     secret = pyotp.random_base32()
-    uri = pyotp.totp.TOTP(secret).provisioning_uri(
-        name=current_user.username,
-        issuer_name="NAS Dashboard"
-    )
+    uri = pyotp.totp.TOTP(secret).provisioning_uri(name=current_user.username, issuer_name="NAS Dashboard")
     return {"secret": secret, "uri": uri}
 
+
 @router.post("/setup-2fa/verify")
-async def verify_2fa_setup(request: Verify2FARequest, current_user = Depends(auth.get_current_user)):
+async def verify_2fa_setup(request: Verify2FARequest, current_user=Depends(auth.get_current_user)):
     """Verify TOTP code and enable 2FA for the user."""
     totp = pyotp.TOTP(request.secret)
     if not totp.verify(request.code):
@@ -34,8 +37,9 @@ async def verify_2fa_setup(request: Verify2FARequest, current_user = Depends(aut
     auth.save_totp_secret(request.secret)
     return {"message": "2FA enabled successfully"}
 
+
 @router.post("/setup-2fa/disable")
-async def disable_2fa(current_user = Depends(auth.get_current_user)):
+async def disable_2fa(current_user=Depends(auth.get_current_user)):
     """Disable 2FA for the user."""
     auth.save_totp_secret("")
     return {"message": "2FA disabled"}