fix: keep full-window dialogs responsive to mouse input

Render feedback, parsing diagnostics, knowledge confirmations, WeChat binding and image preview overlays through body portals so native titlebar drag regions cannot intercept their controls. Preserve themed form styles and modal focus isolation.

Validation: 320 targeted tests, typecheck and lint passed. Native Windows hover and close checks passed for feedback and parsing diagnostics in light and dark themes at two sizes. Full suite timed out without a summary.

Release note: 修复反馈等弹窗与窗口标题栏重叠时，关闭按钮无法正常悬停和点击的问题。

docs/features/in-app-feedback/technical-design.md

@@ -156,6 +156,8 @@ Renderer 不预览、不读取也不接收诊断内容或路径。勾选后详
 ### 3.4 可访问性
 
 - 对话框使用 `role="dialog"`、`aria-modal="true"` 和可见标题。
+- 整窗遮罩通过 React portal 挂到 `document.body`，遵循
+  [全局遮罩与原生拖动区域规则](../../../UI-DESIGN.md#610-应用顶栏与全局操作)。
 - 复用 `activateModalFocus()` 与 `trapTabFocus()`，打开后聚焦反馈类型，关闭后恢复入口
   按钮焦点。
 - 非提交状态支持 Escape 关闭；提交中保持对话框打开，直到请求完成或到达有界超时。