Feat: Rate-limit login endpoint to block brute-force attacks

After LOGIN_MAX_FAILURES consecutive failed attempts from the same source
IP within LOGIN_WINDOW_SECONDS, POST /api/v1/auth/token returns HTTP 429
with a Retry-After header for LOGIN_COOLDOWN_SECONDS. A successful login
resets the counter. Trusted upstream proxy IPs/CIDRs can be declared via
LOGIN_TRUSTED_PROXY_IPS so X-Forwarded-For is honoured correctly behind
nginx ingress or similar reverse proxies.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

api/app/config.py

@@ -18,6 +18,10 @@ class Settings(BaseSettings):
     jwt_expiry_seconds: int = 86400
     owner_username: str
     owner_password: str
+    login_max_failures: int = 5
+    login_window_seconds: int = 300
+    login_cooldown_seconds: int = 900
+    login_trusted_proxy_ips: str = ""
 
 
 @lru_cache