fix: restore consistent controls, usable overlays and narrow layouts

Resolve 15 shared-control, overlay and responsive-layout issues plus the MCP editor being hidden behind settings. Restore theme contrast, danger and disabled states, visible keyboard focus, and consistent Continue fields. Keep the workbar add button reachable and model protocol values readable in narrow containers.

Make nested MCP and image dialogs usable above their parents with focus restoration, keep project Escape handling within the active modal, release native browser views for overlapping help, and restore keyboard access and Escape in sandboxed HTML previews without relaxing sandbox permissions. Add unit and real Electron regression coverage and update design and validation documentation.

Release note: 修复深浅主题下控件边框、危险操作、禁用状态和键盘焦点显示不一致的问题。MCP 编辑器与图片预览可在父弹窗上正常操作，HTML 全屏预览支持键盘进入和 Escape 返回；窄工作栏的添加按钮保持可用，模型连接协议文字完整可读。

Validation: the full suite recorded 5309 passed, 3 failed and 83 skipped. The ProjectSwitcher initial-focus regression was then fixed, and App, ProjectSwitcher and overlay Electron tests passed all 331 cases. The other two HeartbeatCenter failures were reproduced on isolated HEAD 11facf0 and remain pre-existing. Typecheck and lint passed after the fix; staged whitespace checks passed. The full suite was not rerun after the focused fix.

Limits: Electron evidence is from Windows development runs, with fixtures for unrelated services and native occlusion throttling disabled in some drivers. No production build, packaging, macOS/Linux, remote Agent host or external MCP connection validation; skipped tests and the documented scaling and native-select coverage gaps remain.

docs/features/assistant-workbar/browser-tabs-technical-design.md

@@ -81,12 +81,14 @@ Record<ConversationId, Record<BrowserTabId, BrowserLiveState>>
 
 `BrowserViewport` 统一观察 body Portal 的插入、移除和可见属性变化，以及浮层尺寸、
 窗口尺寸、滚动和过渡结束。`browser-viewport-occlusion.ts` 按共享语义识别
-`aria-modal="true"`、dialog、alertdialog、menu 和应用通知：可见应用级 Modal 始终释放
+`aria-modal="true"`、dialog、alertdialog、menu、tooltip 和应用通知：可见应用级 Modal 始终释放
 viewport，其余浮层只在与浏览器区域相交时释放。隐藏节点和隐藏祖先不阻塞浏览器。
 最后一个遮挡消失后，只有当前活动实例恢复同一 viewport 租约；网页、历史和页面状态不变。
 终端关闭确认复用此机制，不再维护单独的隐藏条件。页面无需逐个登记弹窗，也不能靠提高
 CSS `z-index` 覆盖原生子视图。此逻辑仅涉及 Desktop Renderer 的显示租约，不改变
 Runtime、MCP 或远端 Agent 的请求、导航与生命周期。
+同行帮助仍使用 `role="tooltip"`；相交判定使用其内容矩形，不使用铺满窗口的
+`FloatingPortal` 宿主。真实 App 的相交与非相交验证见[浮层审查修复记录](../../quality/overlay-review-2026-09-27.md)。
 
 浏览器应用声明 `visibleAcrossContextSwitches: true`，打开的 Tab 跨项目、会话切换继续显示。
 切换活动 Conversation 不改变当前选中的浏览器或其 `targetRef.conversationId`；用户在会话 B