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/server/src/db/schema.js

@@ -54,6 +54,23 @@ export const likes = pgTable('likes', {
   pk: primaryKey({ columns: [table.userId, table.patchId] }),
 }));
 
+export const customLevels = pgTable('custom_levels', {
+  id: uuid('id').defaultRandom().primaryKey(),
+  worldId: varchar('world_id', { length: 20 }).notNull(),
+  levelId: varchar('level_id', { length: 50 }).unique().notNull(),
+  title: varchar('title', { length: 200 }).notNull(),
+  subtitle: varchar('subtitle', { length: 200 }),
+  description: text('description'),
+  concept: text('concept'),
+  availableModules: text('available_modules').array(),
+  preplacedData: jsonb('preplaced_data'), // imported from sandbox export
+  targetData: jsonb('target_data'),
+  sortOrder: integer('sort_order').default(0),
+  isBoss: boolean('is_boss').default(false),
+  createdAt: timestamp('created_at', { withTimezone: true }).defaultNow().notNull(),
+  updatedAt: timestamp('updated_at', { withTimezone: true }).defaultNow().notNull(),
+});
+
 export const refreshTokens = pgTable('refresh_tokens', {
   id: uuid('id').defaultRandom().primaryKey(),
   userId: uuid('user_id').references(() => users.id, { onDelete: 'cascade' }).notNull(),