feat: fully editable Settings page with service configs, backup/restore, export/import

- Rewrote Settings.jsx: Cell Identity editor, per-service config sections
  (network, wireguard, email, calendar, files, routing, vault) with
  collapsible cards, appropriate input types, and per-section Save buttons
- Added Backup & Restore panel with create/restore/delete actions
- Added Export (download JSON) and Import (upload JSON) panel
- Added PUT /api/config identity field persistence (_identity key in cell_config.json)
  so cell_name/domain/ip_range/wireguard_port survive restarts
- GET /api/config now returns service_configs separately and prefers stored identity
- Added DELETE /api/config/backups/<id> endpoint
- Extended cellAPI in api.js with createBackup, listBackups, restoreBackup,
  deleteBackup, exportConfig, importConfig

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

webui/src/services/api.js

@@ -37,6 +37,12 @@ export const cellAPI = {
   getStatus: () => api.get('/api/status'),
   getConfig: () => api.get('/api/config'),
   updateConfig: (config) => api.put('/api/config', config),
+  createBackup: () => api.post('/api/config/backup'),
+  listBackups: () => api.get('/api/config/backups'),
+  restoreBackup: (id) => api.post(`/api/config/restore/${id}`),
+  deleteBackup: (id) => api.delete(`/api/config/backups/${id}`),
+  exportConfig: (format = 'json') => api.get('/api/config/export', { params: { format } }),
+  importConfig: (config, format = 'json') => api.post('/api/config/import', { config, format }),
 };
 
 // Network Services API