fix: allow Option+Backspace word-delete in input fields

[nwparker]

Summary

• Terminal keyboard handlers for Alt+Backspace and Ctrl+Backspace were registered globally with capture: true, intercepting the events even when focus was in an input or textarea
• This prevented native word-delete (Option+Backspace on macOS) from working in dialogs like Add Worktree
• Now both handlers skip PTY forwarding when the event target is an INPUT or TEXTAREA

Test plan

• Open Add Worktree dialog, type a branch name, use Option+Backspace to delete a word — should work
• Verify Option+Backspace still works in terminal panes (backward-kill-word)
• Check other text inputs (worktree meta dialog, search, settings) also support Option+Backspace

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