feat: 前台页头加明暗切换，刷新图标换成闪电

- settings.site.actions 新增 theme（默认开），后台「操作工具」可关
- 前台页头：月亮/太阳按钮，点击写回 site.theme，前后台同步；
  未登录时不显示（设置接口需要会话）
- 刷新图标 refresh_3_line -> lightning_line，刷新期间仍旋转

src/db/settings.rs

@@ -188,6 +188,9 @@ impl Default for BrandSettings {
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq)]
 #[serde(default)]
 pub struct ActionSettings {
+    /// 明暗切换图标
+    #[serde(default = "default_true")]
+    pub theme: bool,
     /// 刷新图标（重扫本地项目并重拉内容库）
     pub refresh: bool,
     /// 站点设置图标（仅登录后出现）
@@ -199,6 +202,7 @@ pub struct ActionSettings {
 impl Default for ActionSettings {
     fn default() -> Self {
         Self {
+            theme: true,
             refresh: true,
             settings: true,
             session: true,

stash-web/src/AppNext.tsx

@@ -6,6 +6,7 @@ import {
   SearchField,
   Space,
   Toaster,
+  toast,
   type MenuItem,
 } from '@stash/ui'
 import { useEffect, useMemo, useRef, useState } from 'react'
@@ -26,6 +27,7 @@ import { useProjects } from './useProjects'
 import { fetchSession, logout, type SessionState } from './auth'
 import {
   fetchSettings,
+  saveSettings,
   type SettingsDocument,
   type SiteSettings,
 } from './settings'
@@ -287,7 +289,7 @@ export default function AppNext() {
       favicon: '',
       theme: 'auto',
       brand: { name: 'STASH', mark: 'S', logo: '' },
-      actions: { refresh: true, settings: true, session: true },
+      actions: { theme: true, refresh: true, settings: true, session: true },
     },
   }
 
@@ -298,6 +300,27 @@ export default function AppNext() {
     document.documentElement.dataset.scheme = site.site.theme
   }, [site.site.theme])
 
+  /** 当前实际是深色吗（auto 时按系统偏好算） */
+  const isDark =
+    site.site.theme === 'dark' ||
+    (site.site.theme === 'auto' &&
+      window.matchMedia('(prefers-color-scheme: dark)').matches)
+
+  /** 页头的明暗切换：写回站点设置，前后台一起变；只有登录后才会显示 */
+  const toggleTheme = async () => {
+    if (settings === null) return
+    const next = isDark ? 'light' : 'dark'
+    const result = await saveSettings(settings.version, {
+      ...settings.settings,
+      site: { ...settings.settings.site, theme: next },
+    })
+    if (result.ok) {
+      setSettings(result.document)
+      return
+    }
+    toast.error(result.error)
+  }
+
   // 站点级设置：浏览器标签标题与 favicon（空值回落到内置）
   useEffect(() => {
     const title = site.site.title.trim()
@@ -648,6 +671,8 @@ export default function AppNext() {
             authenticated={session?.authenticated === true}
             username={session?.username ?? undefined}
             refreshing={refreshing}
+            dark={isDark}
+            onToggleTheme={() => void toggleTheme()}
             onRefresh={() => {
               refresh()
               load()

stash-web/src/components/admin/AdminNext.tsx

@@ -1935,6 +1935,16 @@ function HeaderPanel({
       <Text size="sm" strong>
         操作工具
       </Text>
+      <div className="sidebar-toggle-row">
+        <Text>明暗切换</Text>
+        <Switch
+          checked={site.actions.theme}
+          onChange={(next) =>
+            onChangeSite({ ...site, actions: { ...site.actions, theme: next } })
+          }
+          label="页头显示明暗切换按钮"
+        />
+      </div>
       <div className="sidebar-toggle-row">
         <Text>刷新</Text>
         <Switch

stash-web/src/components/header/SiteHeader.tsx

@@ -28,7 +28,10 @@ type SiteHeaderProps = {
   username?: string
   /** 刷新中：刷新按钮转圈 */
   refreshing?: boolean
+  /** 当前是否为深色，决定明暗按钮的图标与文案 */
+  dark?: boolean
   onRefresh: () => void
+  onToggleTheme: () => void
   onLogin: () => void
   onLogout: () => void
   onSettings: () => void
@@ -52,7 +55,9 @@ export function SiteHeader({
   authenticated,
   username,
   refreshing = false,
+  dark = false,
   onRefresh,
+  onToggleTheme,
   onLogin,
   onLogout,
   onSettings,
@@ -84,10 +89,17 @@ export function SiteHeader({
       )}
 
       <div className="header-actions">
+        {site.actions.theme && (
+          <IconButton
+            label={dark ? '切换到浅色' : '切换到深色'}
+            icon={<Icon name={dark ? 'sun_line' : 'moon_line'} />}
+            onClick={onToggleTheme}
+          />
+        )}
         {site.actions.refresh && (
           <IconButton
             label="刷新（重扫项目并重拉内容）"
-            icon={<Icon name="refresh_3_line" />}
+            icon={<Icon name="lightning_line" />}
             spinning={refreshing}
             onClick={onRefresh}
           />

stash-web/src/settings.ts

@@ -82,6 +82,8 @@ export type SiteMetaSettings = {
     logo: string
   }
   actions: {
+    /** 明暗切换 */
+    theme: boolean
     /** 刷新图标（重扫本地项目并重拉内容库） */
     refresh: boolean
     /** 站点设置图标 */
@@ -143,7 +145,7 @@ export function defaultSettings(): SiteSettings {
       favicon: '',
       theme: 'auto',
       brand: { name: 'STASH', mark: 'S', logo: '' },
-      actions: { refresh: true, settings: true, session: true },
+      actions: { theme: true, refresh: true, settings: true, session: true },
     },
   }
 }