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

internal/events/hub.go

@@ -13,6 +13,7 @@ import (
 //	changed  笔记内容变化，Rev 为新版本
 //	deleted  笔记被删除
 //	moved    笔记被移动（From -> Path），内容版本不变
+//	settings 应用设置变化，客户端重新读取
 type Event struct {
 	Type string `json:"type"`
 	Path string `json:"path,omitempty"`