[codex] configure TUI terminal opener

[getsolaris]

What changed

• Changed the TUI o shortcut to open the selected worktree root in the OS file manager.
• Kept f as a folder-open alias while updating visible shortcut hints.
• Added t shortcut handling through terminalCommand, with macOS Ghostty inference from TERM_PROGRAM.
• Exposed terminalCommand in the TUI Config view with terminal presets.
• Bumped package version to 1.3.1 for release.

Validation

• bun run typecheck
• bun test (344 pass)
• bun run build
• tmux TUI QA: Config view shows terminalCommand (auto) and saves Ghostty; t uses open -a Ghostty <path> when TERM_PROGRAM=ghostty.