Reusable runner for interactive widget demos.

Handles terminal setup/cleanup, input reading, and the render loop so demo modules can focus purely on widget logic.

Uses OTP 28's :shell.start_interactive({:noshell, :raw}) to switch the terminal to raw mode and read input via IO.getn/2.

Supports Kitty keyboard protocol auto-detection with modifyOtherKeys fallback. Detects synchronized output (mode 2026) support and wraps frames in BSU/ESU when available to eliminate flicker.

Demo Module Protocol

A demo module must implement:

• init(cols, rows) — returns initial state
• handle_event(event, state) — returns {:cont, new_state} or :quit
• render(state) — returns an Element tree
• focused_id(state) — returns the focused widget id or nil