chore: 将登录失败次数上限从 5 提高到 100

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

offline-backend-20260512/backend/app/gateway/routers/auth.py

@@ -336,7 +336,7 @@ def _set_session_cookie(response: Response, token: str, request: Request) -> Non
 # production multi-worker setups, replace this with a shared store (Redis,
 # database-backed counter) to enforce a true per-IP limit.
 
-_MAX_LOGIN_ATTEMPTS = 5
+_MAX_LOGIN_ATTEMPTS = 100
 _LOCKOUT_SECONDS = 300  # 5 minutes
 
 # ip → (fail_count, lock_until_timestamp)