Description

Release 1. A keybind cheatsheet inside the editor (we have 'glint -h' on the CLI). A key (e.g. '?' when not typing, or a Ctrl combo) toggles a centered overlay listing all editor keys and command flags; Esc closes. Source the same content as helpText in main.go (consider sharing a single source of truth).

Acceptance Criteria

• #1 A key toggles a help overlay listing editor keys + commands
• #2 Esc closes it; content matches the CLI help