Add settings page with synced appearance and password change

- Store app settings as one JSON document on the server, merged per key and
  pushed to other devices; cache locally to avoid a flash on load
- Settings page groups appearance, account, shortcuts, shares, API tokens and
  trash; full screen with a section list on phones
- Font size and content width settings
- Change the login password, signing out other sessions
- Settings writes and password changes only accept a login session

web/src/app/events.ts

@@ -1,7 +1,7 @@
 // 订阅服务端的仓库变更事件；断线后指数退避重连，重连成功时触发全量同步
 
 export interface VaultEvent {
-  type: 'tree' | 'changed' | 'deleted' | 'moved'
+  type: 'tree' | 'changed' | 'deleted' | 'moved' | 'settings'
   path?: string
   from?: string
   rev?: string