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-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 = () => {