fix: enforce strict config validation

extensions/imessage/index.ts

@@ -1,4 +1,5 @@
 import type { ClawdbotPluginApi } from "clawdbot/plugin-sdk";
+import { emptyPluginConfigSchema } from "clawdbot/plugin-sdk";
 
 import { imessagePlugin } from "./src/channel.js";
 import { setIMessageRuntime } from "./src/runtime.js";
@@ -7,6 +8,7 @@ const plugin = {
   id: "imessage",
   name: "iMessage",
   description: "iMessage channel plugin",
+  configSchema: emptyPluginConfigSchema(),
   register(api: ClawdbotPluginApi) {
     setIMessageRuntime(api.runtime);
     api.registerChannel({ plugin: imessagePlugin });