feat: synchronize pinned tabs across devices

docs/api.md

@@ -53,6 +53,12 @@ Send `Accept-Language: en` or `Accept-Language: zh-CN` to select the language of
 
 Account language is the `locale` field on `/settings`, supporting only `en` and `zh-CN`. PATCH with `null` removes the override and restores default English. The field is exported, imported, and synchronized with other settings. The sign-in page's temporary choice does not write to the account. Request headers affect only the current response, not account language.
 
+## Pinned tabs
+
+The `/settings` field `pinnedTabs` is an array of Markdown paths relative to the vault. The browser saves pin/unpin actions to the server and restores existing pinned notes on other devices, including after an event connection reconnects. An explicit empty array means no pinned tabs; if the field is absent, the browser migrates its legacy local pins once. Resetting settings stores an empty array so older device caches cannot restore cleared pins. Concurrent replacements of this list use the last server write.
+
+Unpinned tabs and the active tab remain local to each device. Remote unpinning keeps local tabs and unsaved edits open. Explicitly closing a pinned tab also removes its server pin. Renaming notes or folders through the workspace updates pinned paths; unavailable paths are skipped when opening tabs.
+
 ## Browser sign-in
 
 There are no usernames, registration, or roles. Before initialization, `POST /auth/setup` sets the password using `{ password }` and returns a session. An initialized instance cannot be initialized again.

docs/api.zh-CN.md

@@ -53,6 +53,12 @@ curl --fail-with-body \
 
 账户语言位于 `/settings` 的 `locale` 字段，仅支持 `en`、`zh-CN`；PATCH 传 `null` 删除覆盖，恢复默认英文。该字段与其他设置一同导出、导入和同步；登录页的临时选择不写入账户。请求头只影响当前响应，不修改账户语言。
 
+## 固定标签
+
+`/settings` 的 `pinnedTabs` 字段保存相对笔记库的 Markdown 路径数组。浏览器将固定和取消固定写入服务器，其他设备打开时及事件连接重连后会恢复仍存在的固定笔记。显式空数组表示没有固定标签；字段尚不存在时，浏览器会将旧的本地固定标签迁移一次。重置设置会保存空数组，避免其他设备的旧缓存恢复已清空的固定记录。多个设备同时替换该列表时，以服务器最后一次写入为准。
+
+未固定标签和当前选中的标签仍属于各设备本地状态。远程取消固定不会关闭本机标签或丢弃未保存内容；主动关闭固定标签也会移除服务器上的固定记录。通过工作区重命名笔记或目录时会更新固定路径，打开标签时跳过不存在的路径。
+
 ## 浏览器登录
 
 实例没有用户名、注册或角色系统。尚未初始化时，`POST /auth/setup` 使用 `{ password }` 设置密码并返回会话；已经初始化的实例不能再次初始化。