fix(rateLimit): return loopback ip in development to keep rate limiting active

- use `127.0.0.1` as fallback ip when `NODE_ENV === 'development'` in both `getIpFromHeaders` and `getIpFromRequest`
- preserve `unknown` fallback in production to suspend rate limiting when no trusted proxy is configured
- update comments to reflect environment-specific behaviour

src/shared/lib/rateLimit.js

@@ -122,12 +122,12 @@ export function getIpFromHeaders(headersList) {
     const realIp = headersList.get('x-real-ip')?.trim();
     if (realIp && isValidIp(realIp)) return realIp;
   }
-  // Fallback when no trusted proxy is configured.
-  // Callers (router.js, authActions.js) treat 'unknown' as a signal to suspend
-  // rate limiting rather than collapse all traffic into one shared bucket — which
-  // would allow a single attacker to exhaust the quota and deny service globally.
+  // In development, use loopback so rate limiting stays active and the
+  // "IP cannot be determined" warning is not emitted.
+  // In production without a trusted proxy, return 'unknown' to suspend rate
+  // limiting rather than collapse all traffic into one shared bucket.
   // Configure ZEN_TRUST_PROXY=true behind a verified reverse proxy.
-  return 'unknown';
+  return process.env.NODE_ENV === 'development' ? '127.0.0.1' : 'unknown';
 }
 
 /**
@@ -143,7 +143,7 @@ export function getIpFromRequest(request) {
     const realIp = request.headers.get('x-real-ip')?.trim();
     if (realIp && isValidIp(realIp)) return realIp;
   }
-  return 'unknown';
+  return process.env.NODE_ENV === 'development' ? '127.0.0.1' : 'unknown';
 }
 
 /**