auth: fix rate limit bypass, improve error messages

- Disable rate limiting when rate_limit_per_minute = 0
- Add IP lockout mention to 429 response
- Lowercase error messages for consistency
- Raise test mode rate limit 100 -> 10 (more realistic)

src/server/fastapi_app.py

@@ -638,7 +638,7 @@ app.add_middleware(SetupRedirectMiddleware)
 import os
 
 _test_mode = os.getenv("ANIWORLD_TESTING") == "1"
-_auth_rate_limit = 100 if _test_mode else 5
+_auth_rate_limit = 10 if _test_mode else 5
 app.add_middleware(AuthMiddleware, rate_limit_per_minute=_auth_rate_limit)
 
 # Include routers