JavaScript-based find using TreeWalker + <mark> highlights with
match counter, next/previous navigation, and drag-to-corner overlay
matching the existing terminal find bar.
- BrowserFindJavaScript: JS generation for search/next/prev/clear
- BrowserSearchOverlay: SwiftUI overlay with IME-safe onSubmit
- BrowserSearchState: Observable state (needle/selected/total)
- TabManager routing: Cmd+F/G dispatches to browser when focused
- Visibility filter: skips script/style/hidden/aria-hidden elements
- Stale DOM guard: isConnected check in next/previous scripts
- Navigation cleanup: clears find on didFinish and didFailNavigation
Co-authored-by: Lawrence Chen <54008264+lawrencecchen@users.noreply.github.com>
