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/__tests__/plugin-store.test.ts

@@ -48,6 +48,7 @@ function resetStore() {
       'email-footer': [],
       'composer-toolbar': [],
       'sidebar-widget': [],
+      'email-detail-sidebar': [],
       'settings-section': [],
       'context-menu-email': [],
       'navigation-rail-bottom': [],

lib/plugin-api.ts

@@ -113,6 +113,7 @@ export interface PluginAPI {
     registerSettingsSection: (section: SettingsSection) => Disposable;
     registerComposerAction: (action: ComposerAction) => Disposable;
     registerSidebarWidget: (widget: SidebarWidget) => Disposable;
+    registerDetailSidebar: (widget: SidebarWidget) => Disposable;
     registerContextMenuItem: (item: ContextMenuItem) => Disposable;
     registerNavigationRailItem: (component: React.ComponentType) => Disposable;
   };
@@ -556,6 +557,11 @@ export function createPluginAPI(plugin: InstalledPlugin): PluginAPI {
         return registerSlot(plugin.id, 'sidebar-widget', widget.render as React.ComponentType<Record<string, unknown>>, widget.order ?? 100);
       },
 
+      registerDetailSidebar: (widget: SidebarWidget) => {
+        requirePermission(plugin, 'ui:sidebar-widget');
+        return registerSlot(plugin.id, 'email-detail-sidebar', widget.render as React.ComponentType<Record<string, unknown>>, widget.order ?? 100);
+      },
+
       registerContextMenuItem: (item: ContextMenuItem) => {
         requirePermission(plugin, 'ui:context-menu');
         const Component = () => {

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);

lib/plugin-types.ts

@@ -85,6 +85,7 @@ export type SlotName =
   | 'email-footer'
   | 'composer-toolbar'
   | 'sidebar-widget'
+  | 'email-detail-sidebar'
   | 'settings-section'
   | 'context-menu-email'
   | 'navigation-rail-bottom';