fix(gateway): point model override error to config docs

Summary:
- Point allowModelOverride denial errors to the current configuration reference anchor.

Verification:
- Source check: docs/gateway/configuration-reference.md documents plugins.entries.<id>.subagent.allowModelOverride.
- PR CI: gateway tests and required shards succeeded.

src/gateway/server-plugins.test.ts

@@ -968,7 +968,7 @@ describe("loadGatewayPlugins", () => {
         }),
       ),
     ).rejects.toThrow(
-      'plugin "voice-call" is not trusted for fallback provider/model override requests. See https://docs.openclaw.ai/tools/plugin#runtime-helpers and search for: plugins.entries.<id>.subagent.allowModelOverride',
+      'plugin "voice-call" is not trusted for fallback provider/model override requests. See https://docs.openclaw.ai/gateway/configuration-reference#plugins and search for: plugins.entries.<id>.subagent.allowModelOverride',
     );
   });
 

src/gateway/server-plugins.ts

@@ -188,7 +188,7 @@ function authorizeFallbackModelOverride(params: {
       allowed: false,
       reason:
         `plugin "${pluginId}" is not trusted for fallback provider/model override requests. ` +
-        "See https://docs.openclaw.ai/tools/plugin#runtime-helpers and search for: " +
+        "See https://docs.openclaw.ai/gateway/configuration-reference#plugins and search for: " +
         "plugins.entries.<id>.subagent.allowModelOverride",
     };
   }