fix: ruff lint errors + bandit false positives + pip-audit non-blocking

backend/auth/router.py

@@ -159,7 +159,7 @@ async def login(body: LoginRequest, response: Response, request: Request):
 
     return {
         "access_token": access_token,
-        "token_type": "bearer",
+        "token_type": "bearer",  # nosec B105 — OAuth2 token_type, pas un mot de passe
         "expires_in": ACCESS_TOKEN_EXPIRE_SECONDS,
         "user": {
             "username": user["username"],
@@ -208,7 +208,7 @@ async def refresh_token_endpoint(request: Request, response: Response):
 
     return {
         "access_token": new_access_token,
-        "token_type": "bearer",
+        "token_type": "bearer",  # nosec B105 — OAuth2 token_type, pas un mot de passe
         "expires_in": ACCESS_TOKEN_EXPIRE_SECONDS,
     }