feat: Admin SynthQuest level management + user dropdown with admin access

SynthQuest admin:
- New "🎮 SynthQuest" section in admin sidebar
- List custom levels with world, ID, title, patch status
- Create new level: world selector, title, subtitle, description,
  concept (hint), available modules (tag input), boss flag, sort order
- Edit existing levels inline
- Import patch base from sandbox JSON export (📥 button per level)
- Delete levels with confirmation

Server:
- custom_levels table (PostgreSQL)
- CRUD API at /api/v1/admin/levels
- POST /:id/import-patch to import sandbox JSON as preplaced modules

Admin access:
- User badge is now a hover dropdown with "🛠 Admin" + "Cerrar sesion"
- Admin visible in Sandbox toolbar, Workshop nav, and user dropdown
- onSwitchToAdmin passed through navigation chain

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/client/src/services/api.js

@@ -84,6 +84,15 @@ export const workshop = {
   report: (id) => request('POST', `/workshop/${id}/report`),
 };
 
+// Admin Levels
+export const levels = {
+  list: () => request('GET', '/admin/levels'),
+  create: (data) => request('POST', '/admin/levels', data),
+  update: (id, data) => request('PATCH', `/admin/levels/${id}`, data),
+  remove: (id) => request('DELETE', `/admin/levels/${id}`),
+  importPatch: (id, patchData) => request('POST', `/admin/levels/${id}/import-patch`, patchData),
+};
+
 // Admin
 export const admin = {
   stats: () => request('GET', '/admin/stats'),