feat(settings): 侧边栏设置声明式化 — 注册表驱动的开关清单 + 内置支持插头化

- SidebarPrefs 新增 tabsEnabled / viewersEnabled 开放 map（缺省 = 启用），
  PrefsSchema 用 z.dict 校验，旧文档零迁移
- TabDescriptor/FileViewerDescriptor 新增声明式设置面：viewer 补 title/icon，
  两者补 settings.toggles（子代理声明 autoOpenSubagent、终端声明 agentTerminalTools）
- 服务新增 isTabEnabled/isViewerEnabled；openTab 拒绝禁用类型、matchFileViewer
  跳过禁用 viewer
- SideCardSection 重写为注册表驱动清单：侧边栏内容（图标+类型id+开关+嵌套开关）
  + 文件预览（图标+标题+扩展名+开关），开关持久化 + 乐观提交回滚
- 消费点 gating：+ 菜单过滤、子代理自动展开、agent 终端 reconcile、
  产出文件拦截（editor 关闭时回落默认行）、新会话 explorer 预置
- 内置 viewer 补 6 个手绘 outline 图标；store 快照携带 prefs 使开关变更即时生效
- 测试：service gating / builtins 声明 / parsePrefs map 校验 / schema 断言 /
  新增 SideCardSection renderToString 规格
- 文档：README 设置小节、AGENTS.md 描述符与服务方法、新增设计文档；版本 0.5.0

src/client/builtins/tabs.tsx

@@ -80,6 +80,15 @@ export function builtinTabs(ctx: Context): readonly TabDescriptor[] {
       icon: (size: number) => <IconThinkOutline16 size={size} />,
       order: 30,
       single: true,
+      // Declarative settings: the auto-open switch renders under this row in
+      // the Side card settings page (the Subagent page's own related setting).
+      settings: {
+        toggles: [{
+          key: 'autoOpenSubagent',
+          title: () => t('settingsSubagentTitle'),
+          desc: () => t('settingsSubagentDesc'),
+        }],
+      },
       component: ({ ctx, scope, visible, onSubagentJump }) => (
         <SubagentView
           sessionId={scope.sessionId}
@@ -95,6 +104,16 @@ export function builtinTabs(ctx: Context): readonly TabDescriptor[] {
       icon: (size: number) => <IconTerminalOutline16 size={size} />,
       order: 40,
       available: (_ctx, _scope, state) => uiTerminalCount(state) < TERMINAL_LIMIT,
+      // Declarative settings: the model-facing terminal tools switch renders
+      // under this row in the Side card settings page (the Terminal page's
+      // own related setting; the host gates the toolset on it independently).
+      settings: {
+        toggles: [{
+          key: 'agentTerminalTools',
+          title: () => t('settingsToolsTitle'),
+          desc: () => t('settingsToolsDesc'),
+        }],
+      },
       createTab: (state) => {
         const count = uiTerminalCount(state)
         if (count >= TERMINAL_LIMIT) return null

src/client/builtins/viewers.tsx

@@ -5,13 +5,27 @@
  * `binary-download` viewer sniffs NUL bytes via `detect` for unknown
  * binaries and serves doc/xls/ppt by extension; `code` is the catch-all
  * (`exts: []`, lowest priority) that claims any file no other viewer did.
+ *
+ * Every viewer carries the declarative settings-surface fields — `title`
+ * and `icon` — so the Side card settings page can render the enable/disable
+ * inventory without hardcoding (eating our own dogfood).
  */
+import { IconCodeOutline16, IconDownloadOutline16 } from '@deepseek-ai/dsh-client-ui-primitives'
 import { DocxView, XlsxView } from '../office-view.tsx'
 import { PdfView } from '../PdfView.tsx'
 import { PptxView } from '../PptxView.tsx'
 import { TextEditor } from '../TextEditor.tsx'
 import { BinaryDownload } from '../binary-download.tsx'
+import {
+  IconImageOutline16,
+  IconMarkdownOutline16,
+  IconPdfOutline16,
+  IconDocxOutline16,
+  IconXlsxOutline16,
+  IconPptxOutline16,
+} from '../icons.tsx'
 import type { FileViewerDescriptor } from '../service.ts'
+import { t } from '../locales.ts'
 import css from '../sidebar.module.css'
 
 /** The 8 built-in file viewer descriptors. */
@@ -19,6 +33,8 @@ export function builtinViewers(): readonly FileViewerDescriptor[] {
   return [
     {
       id: 'image',
+      title: () => t('viewerImage'),
+      icon: (size: number) => <IconImageOutline16 size={size} />,
       exts: ['png', 'jpg', 'jpeg', 'gif', 'webp', 'svg', 'bmp', 'ico', 'avif'],
       fetchStrategy: 'mediaUrl',
       component: ({ mediaUrl: url, title }) => (
@@ -29,6 +45,8 @@ export function builtinViewers(): readonly FileViewerDescriptor[] {
     },
     {
       id: 'pdf',
+      title: () => t('viewerPdf'),
+      icon: (size: number) => <IconPdfOutline16 size={size} />,
       exts: ['pdf'],
       fetchStrategy: 'mediaUrl',
       component: ({ scope, path, title }) => (
@@ -37,6 +55,8 @@ export function builtinViewers(): readonly FileViewerDescriptor[] {
     },
     {
       id: 'docx',
+      title: () => t('viewerDocx'),
+      icon: (size: number) => <IconDocxOutline16 size={size} />,
       exts: ['docx'],
       fetchStrategy: 'mediaUrl',
       component: ({ scope, path, title }) => (
@@ -45,6 +65,8 @@ export function builtinViewers(): readonly FileViewerDescriptor[] {
     },
     {
       id: 'xlsx',
+      title: () => t('viewerXlsx'),
+      icon: (size: number) => <IconXlsxOutline16 size={size} />,
       exts: ['xlsx'],
       fetchStrategy: 'mediaUrl',
       component: ({ scope, path, title }) => (
@@ -53,6 +75,8 @@ export function builtinViewers(): readonly FileViewerDescriptor[] {
     },
     {
       id: 'pptx',
+      title: () => t('viewerPptx'),
+      icon: (size: number) => <IconPptxOutline16 size={size} />,
       exts: ['pptx'],
       fetchStrategy: 'mediaUrl',
       component: ({ scope, path, title }) => (
@@ -61,12 +85,16 @@ export function builtinViewers(): readonly FileViewerDescriptor[] {
     },
     {
       id: 'markdown',
+      title: () => t('viewerMarkdown'),
+      icon: (size: number) => <IconMarkdownOutline16 size={size} />,
       exts: ['md', 'markdown'],
       fetchStrategy: 'fsRead',
       component: (props) => <TextEditor {...props} />,
     },
     {
       id: 'code',
+      title: () => t('viewerCode'),
+      icon: (size: number) => <IconCodeOutline16 size={size} />,
       exts: [],
       priority: -100,
       fetchStrategy: 'fsRead',
@@ -74,6 +102,8 @@ export function builtinViewers(): readonly FileViewerDescriptor[] {
     },
     {
       id: 'binary-download',
+      title: () => t('viewerBinary'),
+      icon: (size: number) => <IconDownloadOutline16 size={size} />,
       exts: ['doc', 'xls', 'ppt'],
       priority: -50,
       fetchStrategy: 'binary-download',