feat: 内置 HTML 预览器 + 沙箱浏览器 tab（v0.5.0）

- html viewer：.html/.htm 沙箱 iframe 预览（相对资源经 /sidebar/html 路径编码路由加载，CSP sandbox + 信任围栏 + cwd 边界），预览/编辑切换
- browser tab：+ 菜单多开（browser:<n>），地址栏后退/前进/刷新/在浏览器中打开（15px 图标），URL 与标题按会话持久化（patchTab + nextBrowser）
- 安全：iframe 一律不透明源沙箱（无 allow-same-origin/top-navigation、no-referrer、权限策略全禁、禁 srcdoc）；地址栏仅 http(s)、拒绝 localhost 等本机地址；界面实时沙箱状态（关闭红色警示）+ 临时解锁/恢复
- 设置：htmlViewerNoSandbox / htmlViewerDefaultUnsafe / browserNoSandbox / browserInterceptLinks 四个声明式二级设置（默认安全）
- 外链拦截：聊天/界面 http(s) 外链默认在侧边栏打开（openTab seed.url），Ctrl/Cmd 点击放行
- 嵌入拒绝面板：browser.probe 路由探测 X-Frame-Options/frame-ancestors，被拒站点显示原因 + 在浏览器中打开/仍然加载
- 设置页可滚动；内置 7 tab + 9 viewer；新增设计文档；268 个测试全绿

src/client/locales.ts

@@ -136,6 +136,33 @@ const zh = {
   viewerMarkdown: 'Markdown',
   viewerCode: '代码',
   viewerBinary: '二进制下载',
+  viewerHtml: 'HTML',
+  browser: '浏览器',
+  browserPlaceholder: '输入网址，例如 example.com',
+  browserGo: '前往',
+  browserBack: '后退',
+  browserForward: '前进',
+  browserStart: '输入网址开始浏览（沙箱模式）',
+  browserBlockedScheme: '已阻止：仅支持 http/https 链接',
+  browserBlockedLoopback: '已阻止：不允许在浏览器中访问本机或内部地址',
+  browserInvalid: '无效的网址',
+  browserNoSandboxWarning: '沙箱已关闭：当前页面与界面同源，拥有完整会话权限（可在设置中恢复）',
+  htmlNoSandboxWarning: '沙箱已关闭：此 HTML 与界面同源，可读取会话文件与内部接口（可在设置中恢复）',
+  sandboxStatusOn: '沙箱模式：已启用 · 页面无法访问界面数据与本地文件，登录态与第三方 Cookie 可能不可用',
+  sandboxUnlock: '临时解锁（不安全）',
+  sandboxRestore: '恢复沙箱',
+  settingsHtmlDefaultUnsafeTitle: 'HTML 预览默认以非沙箱模式打开（不安全）',
+  settingsHtmlDefaultUnsafeDesc: '开启后，每次打开 HTML 文件时预览默认处于非沙箱状态（与界面同源，可读取会话文件与内部接口）；可在状态行临时恢复沙箱',
+  settingsHtmlSandboxTitle: '关闭 HTML 预览沙箱（不安全）',
+  settingsHtmlSandboxDesc: '关闭后，预览的 HTML 将与界面同源运行，可读取会话文件、本地存储并调用内部接口。仅对完全可信的文件开启',
+  settingsBrowserSandboxTitle: '关闭浏览器沙箱（不安全）',
+  settingsBrowserSandboxDesc: '关闭后，访问的任何网站都将与界面同源运行，可读取会话数据并冒充你的登录状态。仅对完全可信的站点开启',
+  settingsBrowserLinksTitle: '聊天区外链在侧边栏打开',
+  settingsBrowserLinksDesc: '开启后，点击聊天或界面中的 http/https 外链时在侧边栏浏览器中打开，不再弹出新窗口；Ctrl/Cmd 点击可临时放行',
+  browserOpenExternal: '在浏览器中打开',
+  browserEmbedBlocked: '{host} 拒绝了嵌入请求',
+  browserEmbedBlockedDesc: '该站点通过 X-Frame-Options / frame-ancestors 禁止在其它页面中显示，无法在侧边栏内加载。可在浏览器中直接打开',
+  browserEmbedAnyway: '仍然加载',
   subagent: '子代理',
   openSubagent: '子代理',
   subagentMainAgent: '主代理',
@@ -284,6 +311,33 @@ const en: Record<keyof typeof zh, string> = {
   viewerMarkdown: 'Markdown',
   viewerCode: 'Code',
   viewerBinary: 'Binary download',
+  viewerHtml: 'HTML',
+  browser: 'Browser',
+  browserPlaceholder: 'Enter a URL, e.g. example.com',
+  browserGo: 'Go',
+  browserBack: 'Back',
+  browserForward: 'Forward',
+  browserStart: 'Enter a URL to start browsing (sandbox mode)',
+  browserBlockedScheme: 'Blocked: only http/https URLs are allowed',
+  browserBlockedLoopback: 'Blocked: local and internal addresses cannot be browsed here',
+  browserInvalid: 'Invalid URL',
+  browserNoSandboxWarning: 'Sandbox off: the current page runs with full GUI privileges (re-enable in settings)',
+  htmlNoSandboxWarning: 'Sandbox off: this HTML runs with full GUI privileges (re-enable in settings)',
+  sandboxStatusOn: 'Sandbox mode: on · pages cannot access the GUI\'s data or local files; logins and third-party cookies may not work',
+  sandboxUnlock: 'Temporarily disable (unsafe)',
+  sandboxRestore: 'Restore sandbox',
+  settingsHtmlDefaultUnsafeTitle: 'Open HTML previews unsandboxed by default (unsafe)',
+  settingsHtmlDefaultUnsafeDesc: 'When on, every newly opened HTML preview starts in the unsandboxed state (same origin as the GUI — it can read session files and internal APIs); the status row still offers a one-tap restore',
+  settingsHtmlSandboxTitle: 'Disable HTML preview sandbox (unsafe)',
+  settingsHtmlSandboxDesc: 'With the sandbox off, previewed HTML runs with the same origin as the GUI: it can read session files, local storage and call internal APIs. Only enable for fully trusted files',
+  settingsBrowserSandboxTitle: 'Disable browser sandbox (unsafe)',
+  settingsBrowserSandboxDesc: 'With the sandbox off, any visited site runs with the same origin as the GUI: it can read session data and act as your logged-in session. Only enable for fully trusted sites',
+  settingsBrowserLinksTitle: 'Open chat external links in the sidebar',
+  settingsBrowserLinksDesc: 'When on, clicking an http/https external link in the chat or GUI opens the sidebar browser instead of a new window; Ctrl/Cmd+click always bypasses',
+  browserOpenExternal: 'Open in browser',
+  browserEmbedBlocked: '{host} refused to be embedded',
+  browserEmbedBlockedDesc: 'The site forbids being displayed inside other pages (X-Frame-Options / frame-ancestors), so it cannot load in the sidebar. Open it directly in your browser instead.',
+  browserEmbedAnyway: 'Load anyway',
   subagent: 'Subagents',
   openSubagent: 'Subagents',
   subagentMainAgent: 'Main agent',