feat(config): gate channel config writes

src/config/types.imessage.ts

@@ -6,6 +6,8 @@ export type IMessageAccountConfig = {
   name?: string;
   /** Optional provider capability tags used for agent/runtime guidance. */
   capabilities?: string[];
+  /** Allow channel-initiated config writes (default: true). */
+  configWrites?: boolean;
   /** If false, do not start this iMessage account. Default: true. */
   enabled?: boolean;
   /** imsg CLI binary path (default: imsg). */