feat: add hotel_admin (Системный администратор) and technician roles + protect hotel owner from deletion

- Migration 035: extend role constraint to include hotel_admin and technician; migrate existing manager users to hotel_admin
- auth.ts: registration now assigns hotel_admin (not manager) to hotel owner
- seed.ts: demo user manager@grand-palace.ru seeded as hotel_admin
- types.ts: expand JwtPayload role union with all roles
- users.ts: hotel_admin included in access checks; role creation/edit/delete rules enforced; hotel_admin users are undeletable and uneditable (non-super_admin); role cannot be set to hotel_admin via PATCH
- rooms.ts / channels.ts: hotel_admin added to write-access checks
- UsersPage.tsx: hotel_admin and technician added to StaffRole, ROLE_META, DEFAULT_POSITIONS, mapRole, backendRoleMap, INITIAL_ROLE_PERMISSIONS; delete button hidden for hotel_admin; role selector locked for hotel_admin users; hotel_admin excluded from new-user role selector

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/src/types.ts

@@ -2,7 +2,7 @@ export interface JwtPayload {
   sub: string         // user.id (UUID)
   email: string
   name: string
-  role: 'manager' | 'housekeeper' | 'super_admin'
+  role: 'hotel_admin' | 'manager' | 'housekeeper' | 'super_admin' | 'receptionist' | 'accountant' | 'security' | 'technician'
   hotelId: string | null
   hotelSlug: string | null
 }