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/auth.py

@@ -1,16 +1,18 @@
 """Core authentication endpoints: login, token refresh, user info, proxy auth."""
-from datetime import timedelta
+
 import asyncio
+import logging
+from datetime import timedelta
+
 import httpx
-from typing import Optional
-from fastapi import APIRouter, Body, Depends, HTTPException, status, Request, Response
+import jwt
+from fastapi import APIRouter, Body, Depends, HTTPException, Request, Response, status
 from pydantic import BaseModel
 from slowapi import Limiter
 from slowapi.util import get_remote_address
-import jwt
-import config
+
 import auth_service as auth
-import logging
+import config
 
 logger = logging.getLogger(__name__)
 router = APIRouter()
@@ -40,7 +42,7 @@ def _set_auth_response_tokens(response: Response, access_token: str, refresh_tok
     auth.set_auth_cookies(response, access_token, refresh_token)
 
 
-def _extract_refresh_token(request: Request, req: Optional[RefreshRequest] = None) -> str:
+def _extract_refresh_token(request: Request, req: RefreshRequest | None = None) -> str:
     cookie_token = request.cookies.get(auth.REFRESH_COOKIE_NAME, "")
     if cookie_token:
         return cookie_token
@@ -87,7 +89,7 @@ async def send_failed_login_alert(ip_address: str, username: str, reason: str):
             res = await client.post(
                 f"https://api.telegram.org/bot{config.TELEGRAM_BOT_TOKEN}/sendMessage",
                 data={"chat_id": config.TELEGRAM_CHAT_ID, "text": msg, "parse_mode": "Markdown"},
-                timeout=10.0
+                timeout=10.0,
             )
             logger.info("Telegram alert sent, status: %s", res.status_code)
     except Exception as e:
@@ -147,6 +149,7 @@ async def proxy_auth(request: Request, response: Response):
     """Auto-login when Authelia has already authenticated the user via forward-auth.
     Caddy sets Remote-User and Remote-Groups headers after successful Authelia verification."""
     from rbac import resolve_role
+
     if not config.is_trusted_proxy(request.client.host):
         logger.warning(f"Rejected proxy auth attempt from unauthorized IP: {request.client.host}")
         raise HTTPException(status_code=403, detail="Unauthorized proxy source")
@@ -196,7 +199,7 @@ async def read_users_me(current_user=Depends(auth.get_current_user)):
 
 @router.post("/refresh")
 @limiter.limit("10/minute")
-async def refresh_token(request: Request, response: Response, req: Optional[RefreshRequest] = Body(default=None)):
+async def refresh_token(request: Request, response: Response, req: RefreshRequest | None = Body(default=None)):
     refresh_token_value = _extract_refresh_token(request, req)
     access_token, refresh_token = await _refresh_tokens_from_value(refresh_token_value)
     _set_auth_response_tokens(response, access_token, refresh_token)
@@ -232,6 +235,7 @@ async def rbac_config(current_user=Depends(auth.get_current_user)):
     if current_user.role != "admin":
         raise HTTPException(status_code=403, detail="Admin only")
     from rbac import load_rbac
+
     return load_rbac()
 
 
@@ -240,6 +244,7 @@ async def rbac_set_override(username: str, request: Request, current_user=Depend
     if current_user.role != "admin":
         raise HTTPException(status_code=403, detail="Admin only")
     from rbac import update_rbac
+
     body = await request.json()
     pages = body.get("pages")
     if pages is None:
@@ -257,6 +262,7 @@ async def rbac_set_override(username: str, request: Request, current_user=Depend
 @router.get("/preferences")
 async def get_preferences(current_user=Depends(auth.get_current_user)):
     from rbac import get_sidebar_order
+
     order = get_sidebar_order(current_user.username)
     return {"sidebar_order": order}
 
@@ -264,7 +270,9 @@ async def get_preferences(current_user=Depends(auth.get_current_user)):
 @router.put("/preferences")
 async def save_preferences(request: Request, current_user=Depends(auth.get_current_user)):
     import traceback
+
     from rbac import save_sidebar_order
+
     try:
         body = await request.json()
         order = body.get("sidebar_order")
@@ -298,6 +306,7 @@ async def rbac_update_role(role: str, request: Request, current_user=Depends(aut
     if current_user.role != "admin":
         raise HTTPException(status_code=403, detail="Admin only")
     from rbac import update_rbac
+
     body = await request.json()
     pages = body.get("pages")
     sidebar_links = body.get("sidebar_links")