[Pepps233]

Summary

Pause editor cursor blinking when the terminal window or pane is not focused.

Reasoning

Input activity cannot reliably indicate focus because an active user may be reading or waiting. The TUI now uses standard terminal focus reports and treats unavailable tmux focus reporting conservatively.

Changes

• centralize terminal focus tracking for regular and fullscreen TUI renderers
• stop placeholder cursor animation and hide the hardware cursor while unfocused
• keep the software cursor static when tmux cannot report focus changes
• preserve fullscreen selection cleanup on focus loss
• document the tmux focus-events setting
• add terminal, editor, renderer, and fallback regression coverage

User impact

The placeholder cursor blinks in focused terminals and panes, stays visible without animation when unfocused, and remains static when reliable focus reporting is unavailable. tmux users can enable focused-pane animation with set -g focus-events on.

Testing

• npm run check
• ./test.sh
• cd packages/tui && node --test test/terminal.test.ts test/editor-placeholder-cursor.test.ts test/tui-focus.test.ts test/tui-alt-screen.test.ts

[Issacboy123]

This PR looks good to me, handles focus well in various terminals for the cursor to either be blinking or not.