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/preload.js

@@ -135,7 +135,11 @@ const ALLOWED_SEND_CHANNELS = [
   'export',
 
   // Git diff
-  'git-diff'
+  'git-diff',
+
+  // Plugin settings
+  'plugin-settings:get',
+  'plugin-settings:set'
 ];
 
 const ALLOWED_RECEIVE_CHANNELS = [