feat(doc-editor): QuickSearchBar inline overlay replaces floating find dialog

[abbaye]

Context

The document editor previously used a floating DocumentFindReplaceDialog window for Ctrl+F / Ctrl+H. This has been replaced with an inline QuickSearchBar overlay consistent with the rest of the IDE.

What changed

• Added DocumentSearchTarget : ISearchTarget adapter over DocumentSearchViewModel
• Added QuickSearchBar + Canvas overlay to DocumentTextPane.xaml
• Exposed ShowQuickSearch() / HideQuickSearch() on DocumentTextPane
• Ctrl+F and Ctrl+H now show the inline overlay instead of the floating window
• Removed DocumentFindReplaceDialog usage and _findDialog field from DocumentEditorHost

Files affected

• DocumentTextPane.xaml / .xaml.cs
• DocumentEditorHost.xaml.cs
• ViewModels/DocumentSearchTarget.cs (new)

Status

Implemented in commit 50c48e4b on branch Dev2026-05-03.

Follow-up

• Verify overlay dismisses on Escape
• Verify Replace All reports match count in status bar
• Remove DocumentFindReplaceDialog class if fully orphaned