Waiter PWA: sub-choices in modal, zone filter, login JSON fix

ItemOptionsModal:
- Supports inline sub-choices on both preference choices and checkbox options;
  sub-choices appear indented when the parent is selected
- Supports shared_subset at the preference-set level (shown unless the selected
  choice has disables_subset)
- Pre-selects default choices and their default sub-choices on open
- Add button disabled + red validation hints until all required selections made
- Price total reflects sub-choice extra_cost

TableListPage:
- Zone filter dropdown with multi-select; filters by table group_id
  (fetches /api/tables/groups alongside tables and orders)
- Fixed 'mine' and 'free' filters to compose correctly with zone filter

LoginPage:
- Switch to JSON body { username, pin } to match updated /api/auth/login
- Read user fields from data.user.* instead of flat response

vite.config.js: enable SW devOptions so PWA works in dev mode

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

waiter_pwa/vite.config.js

@@ -23,6 +23,9 @@ export default defineConfig({
         globPatterns: ['**/*.{js,css,html,ico,png,svg}'],
         runtimeCaching: [],
       },
+      devOptions: {
+        enabled: true,
+      },
     }),
   ],
 })