feat: add plugin/theme harness and admin dashboard

Plugin & Theme System:
- Add plugin type definitions, permissions (30+), and validation constants
- Add IndexedDB storage layer for plugin code, theme CSS, and previews
- Add theme CSS sanitization, injection, and safety validation
- Add HookBus event system with 130+ hooks across 20 domains
- Add plugin ZIP extraction and manifest validation with JS security checks
- Add sandboxed PluginAPI factory with scoped storage, logging, and permission gating
- Add plugin loader with blob URL dynamic import and auto-disable circuit breaker
- Add 3 built-in themes (Nord, Catppuccin, Solarized)
- Add Zustand plugin store with install/uninstall/enable/disable lifecycle
- Add PluginSlot, PluginSlotRenderer, and PluginErrorBoundary components
- Add plugins and themes settings UI panels
- Integrate plugin slots into email viewer, composer, navigation rail, sidebar, and context menu
- Extend theme store with custom theme installation and activation

Admin Dashboard:
- Add admin authentication with scrypt password hashing and AES-256-GCM sessions
- Add rate-limited login (5 attempts/15min per IP)
- Add config manager with admin override > env var > default priority
- Add settings policy system with feature gates and per-setting restrictions
- Add audit logging with rotation
- Add admin API routes (login, logout, config, policy, audit, password change)
- Add admin UI pages (login, dashboard, config, policy, audit)
- Add policy store for client-side feature gate enforcement
- Wire admin password initialization into server instrumentation

Tests:
- Add 139 tests across 10 test files covering all plugin/theme modules

components/email/email-composer.tsx

@@ -18,6 +18,7 @@ import { useSettingsStore } from "@/stores/settings-store";
 import { buildMimeMessage, wrapCmsAsSmimeMessage } from "@/lib/smime/mime-builder";
 import type { MimeAttachment } from "@/lib/smime/mime-builder";
 import { smimeSign } from "@/lib/smime/smime-sign";
+import { PluginSlot } from "@/components/plugins/plugin-slot";
 import { smimeEncrypt } from "@/lib/smime/smime-encrypt";
 import { useContactStore } from "@/stores/contact-store";
 import { useTemplateStore } from "@/stores/template-store";
@@ -1237,6 +1238,7 @@ export function EmailComposer({
                 </Button>
               </>
             )}
+            <PluginSlot name="composer-toolbar" />
           </div>
 
           {/* Right side - Discard + Send (desktop) */}

components/email/email-context-menu.tsx

@@ -9,6 +9,7 @@ import {
   ContextMenuSubMenu,
   ContextMenuHeader,
 } from "@/components/ui/context-menu";
+import { PluginSlot } from "@/components/plugins/plugin-slot";
 import {
   Reply,
   ReplyAll,
@@ -366,6 +367,8 @@ export function EmailContextMenu({
           )
         }
       />
+
+      <PluginSlot name="context-menu-email" />
     </ContextMenu>
   );
 }

components/email/email-viewer.tsx

@@ -95,6 +95,7 @@ import type { SmimeStatus } from "@/lib/smime/types";
 import { parseTnef, isTnefAttachment } from "@/lib/tnef";
 import { debug } from "@/lib/debug";
 import type { TnefAttachment } from "@/lib/tnef";
+import { PluginSlot } from "@/components/plugins/plugin-slot";
 
 interface EmailViewerProps {
   email: Email | null;
@@ -2819,6 +2820,7 @@ export function EmailViewer({
           {showToolbarLabels && <span className="hidden sm:inline text-sm">{t('forward')}</span>}
         </Button>
         </>)}
+        <PluginSlot name="toolbar-actions" />
       </div>
 
       {/* Right: Organize actions — order: archive, delete, move, star, tag, spam, read state, print, view source */}
@@ -4443,6 +4445,8 @@ export function EmailViewer({
 
         <div>
 
+          <PluginSlot name="email-banner" />
+
           {/* Email Body */}
           <div className="email-content-wrapper overflow-x-auto">
             {effectiveEmailContent.isHtml ? (
@@ -4470,6 +4474,8 @@ export function EmailViewer({
             )}
           </div>
 
+          <PluginSlot name="email-footer" />
+
           {/* Quick Reply Section - hidden for drafts */}
           {!isDraft && (<div className={cn(
             "mt-6 mx-6 mb-6 bg-background rounded-lg shadow-sm border transition-all",