polish(web): 打磨 Web 会话界面的布局、自适应与组件一致性

1. 统一会话列宽度轴：新增 --dsh-chat-content-width（748px），输入框、todo、goal、queue、approval、plan review、ask question 等容器的宽度与边距全部由该变量推导，消除各面板之间的像素漂移，窄视口下的边缘留白也保持一致。
2. 输入框自适应与细节：控制行改为容器查询（460px 阈值以下权限选择器只显示图标+下拉，隐藏文字）；卡片圆角 20→22、行内边距调整并整体下移 2px（发送按钮除外）；permission/model 触发器统一 24px 圆角；Plan 与 Read Only 间距 +8。
3. 修复浮层菜单溢出：slash 菜单与命令弹层钳制到输入卡片宽度，超长行以省略号截断；Tooltip 增加 12px 视口边缘安全距离。
4. 增加与替换图标：Add provider 改用输入框同款加号图标（IconPlusOutline16），统一图标尺寸与字号。
5. 统一 Settings → Models 组件：补齐按钮 hover 态、select 下拉箭头不再贴边、标题区与 provider 卡片间距 +12。
6. 侧边栏交互：add workspace / group by / create session / 收起侧边栏四个图标按钮增加 500ms 延迟 tooltip（前两个向下弹出）；展开态的 New Session 不再重复显示 tooltip；侧边栏窄屏自适应收起逻辑微调。
7. 其他：hero 区 workspace 徽章右移对齐；附带 Agent Note（中英双语）记录共享宽度轴与容器查询的设计取舍。

packages/client/ui-layout/tests/layout-store.spec.ts

@@ -17,9 +17,9 @@ const PERSIST_KEY = 'dsh.layout.panels'
 beforeEach(() => { localStorage.clear() })
 
 describe('createLayoutStore', () => {
-  it('initializes the sidebar at its default width and details closed', () => {
+  it('initializes the sidebar at its default width, details closed, wide viewport assumed', () => {
     const { store } = createLayoutStore().create()
-    expect(store.getSnapshot()).toEqual({ sidebar: SIDEBAR_DEFAULT, details: 0 })
+    expect(store.getSnapshot()).toEqual({ sidebar: SIDEBAR_DEFAULT, details: 0, narrow: false, narrowExpanded: false })
   })
 
   it('each create() is an independent instance (factory is not a singleton)', () => {
@@ -50,6 +50,30 @@ describe('createLayoutStore', () => {
     expect(store.getSnapshot().sidebar).toBe(SIDEBAR_DEFAULT)
   })
 
+  it('narrow toggleSidebar flips only the re-expand override; the width preference survives', () => {
+    const { store, actions } = createLayoutStore().create()
+    actions.setSidebar(400)
+    actions.setNarrow(true)
+    actions.toggleSidebar()
+    expect(store.getSnapshot()).toEqual({ sidebar: 400, details: 0, narrow: true, narrowExpanded: true })
+    actions.toggleSidebar()
+    expect(store.getSnapshot().narrowExpanded).toBe(false)
+    expect(store.getSnapshot().sidebar).toBe(400)
+  })
+
+  it('crossing the breakpoint drops the override; a same-value setNarrow keeps it', () => {
+    const { store, actions } = createLayoutStore().create()
+    actions.setNarrow(true)
+    actions.toggleSidebar()
+    expect(store.getSnapshot().narrowExpanded).toBe(true)
+    actions.setNarrow(true)
+    expect(store.getSnapshot().narrowExpanded).toBe(true)
+    actions.setNarrow(false)
+    expect(store.getSnapshot()).toMatchObject({ narrow: false, narrowExpanded: false })
+    actions.setNarrow(true)
+    expect(store.getSnapshot().narrowExpanded).toBe(false)
+  })
+
   it('openDetails uses the contract default, preserves an open width, and closeDetails zeroes', () => {
     const { store, actions } = createLayoutStore().create()
     actions.openDetails()
@@ -72,6 +96,8 @@ describe('createLayoutStore', () => {
     expect(second.store.getSnapshot()).toEqual({
       sidebar: SIDEBAR_DEFAULT,
       details: 0,
+      narrow: false,
+      narrowExpanded: false,
     })
   })
 })