refactor: route channel runtime via plugin api

extensions/imessage/index.ts

@@ -1,12 +1,14 @@
 import type { ClawdbotPluginApi } from "clawdbot/plugin-sdk";
 
 import { imessagePlugin } from "./src/channel.js";
+import { setIMessageRuntime } from "./src/runtime.js";
 
 const plugin = {
   id: "imessage",
   name: "iMessage",
   description: "iMessage channel plugin",
   register(api: ClawdbotPluginApi) {
+    setIMessageRuntime(api.runtime);
     api.registerChannel({ plugin: imessagePlugin });
   },
 };