feat: #61 Plugin system — backend API, sandboxed Web Worker, hooks wired to real app flow, user guide, 47+21 tests

frontend/js/app.js

@@ -22,6 +22,7 @@ import { initMermaid, setupFocusMode } from './mermaid-viewer.js';
 import PaneManager from './pane-manager.js';
 import { initDesktopIntegration, isTauriEnv } from './desktop.js';
 import { initPush } from './push.js';
+import { initPlugins } from './plugins.js';
 
 // =========================================================================
 // Initialization — mirrors the original app.js init() ordering
@@ -68,8 +69,9 @@ async function init() {
   UI.TabManager.init();
   PaneManager.init();
   initCommandPalette();
-    initMobileToolbar();
-    initPush();
+      initMobileToolbar();
+      initPush();
+      initPlugins();
 
   if (authOk) {
     Legacy.initSyncStatus();