feat(plugins): resizable collapsible detail sidebar, auto-init on refresh

- Add email-detail-sidebar slot type for right-side plugin panels
- Plugin sidebar inside EmailViewer with ResizeHandle (200-500px, drag/dbl-click reset)
- Collapse/expand toggle with PanelRightClose/PanelRightOpen icons
- Call initializePlugins() on mount so plugins survive page refresh
- Fix plugin loader: call exposePluginExternals() before loading
- Fix CSP: add blob: to script-src for plugin bundle loading
- Fix enablePlugin: wire slot registration bridge before loading
- Fix email-banner PluginSlot: pass email via extraProps
- Fix sidebar-widget PluginSlot: move inside scrollable area
- Emit emailHooks.onEmailOpen/onEmailClose from selectEmail()

lib/plugin-loader.ts

@@ -49,6 +49,9 @@ export async function loadPlugin(plugin: InstalledPlugin): Promise<void> {
     return;
   }
 
+  // Ensure React/ReactDOM are exposed before any plugin module evaluates
+  exposePluginExternals();
+
   try {
     // 1. Read bundle from IndexedDB
     const code = await pluginStorage.getCode(plugin.id);