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/routes/auth.ts

@@ -168,7 +168,7 @@ const auth: FastifyPluginAsync = async (fastify) => {
         )
         await client.query(
           `INSERT INTO users (name, email, password_hash, role, hotel_id, phone, email_confirmed, confirmation_token, confirmation_sent_at)
-           VALUES ($1, $2, $3, 'manager', $4, $5, false, $6, NOW())`,
+           VALUES ($1, $2, $3, 'hotel_admin', $4, $5, false, $6, NOW())`,
           [contact, email.toLowerCase().trim(), passwordHash, hotel.id, phone ?? null, confirmToken],
         )
         await client.query('COMMIT')