fix(gateway): reject known-weak placeholder credentials at startup

Port from openclaw/openclaw#64586: users who copy .env.example without
changing placeholder values now get a clear error at startup instead of
a confusing auth failure from the platform API. Also rejects placeholder
API_SERVER_KEY when binding to a network-accessible address.

Cherry-picked from PR #8677.

gateway/platforms/api_server.py

@@ -1819,6 +1819,23 @@ class APIServerAdapter(BasePlatformAdapter):
                 )
                 return False
 
+            # Refuse to start network-accessible with a placeholder key.
+            # Ported from openclaw/openclaw#64586.
+            if is_network_accessible(self._host) and self._api_key:
+                try:
+                    from hermes_cli.auth import has_usable_secret
+                    if not has_usable_secret(self._api_key, min_length=8):
+                        logger.error(
+                            "[%s] Refusing to start: API_SERVER_KEY is set to a "
+                            "placeholder value. Generate a real secret "
+                            "(e.g. `openssl rand -hex 32`) and set API_SERVER_KEY "
+                            "before exposing the API server on %s.",
+                            self.name, self._host,
+                        )
+                        return False
+                except ImportError:
+                    pass
+
             # Port conflict detection — fail fast if port is already in use
             try:
                 with _socket.socket(_socket.AF_INET, _socket.SOCK_STREAM) as _s: