feat(plugins): wire plugin system into app initialization

- Add plugin system bootstrap in renderer.js after sidebar/commands init
- Wire status bar DOM insertion, editor API, and IPC adapters
- Add plugin-settings:get/set IPC channels to preload allowlist
- Add IPC handlers in main process using existing settings store
- Fix eqeqeq warning in EventBus.hasHandler

Amit Haridas

src/plugins/event-bus.js

@@ -36,7 +36,7 @@ class EventBus {
 
   hasHandler(event) {
     const handlers = this.listeners.get(event);
-    return handlers != null && handlers.length > 0;
+    return handlers !== undefined && handlers !== null && handlers.length > 0;
   }
 }