Fix tmux detach focus regression on Windows (#1587)

[binaricat]

Summary

• Replace native window.confirm() with an in-app confirm dialog for tmux detach, avoiding broken Radix modal/focus state on Windows Electron
• Defer terminal refocus after detach and restore cursor blink plus xterm focus via a session restore event
• Fixes sidebar tmux "new session" becoming unusable and terminal cursor blink stopping after detach

Test plan

• On Windows, connect SSH and create a tmux session
• Use sidebar System → tmux → Detach all
• Verify terminal cursor blinks and input works
• Click sidebar tmux New (+) and create another session successfully
• Run npm test for tmuxActionFocus.test.ts and focusTerminalSession.test.ts

Fixes #1587

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