Show a web UI in a terminal: CDP screencast plus kitty graphics

To run a browser-based tool (e.g. a webview waveform viewer) inside a terminal, use the pattern cmux-tui's browser panes use. Start headless Chrome, set device metrics from the terminal's cell size times its cell pixel size, and stream frames with Page.startScreencast (Page.screencastFrame PNGs). Draw each frame with the kitty graphics protocol, and send mouse, wheel and key input back over CDP (Input.dispatchMouseEvent, Input.insertText). Catches: the terminal must support kitty graphics (kitty, Ghostty, WezTerm do; GNOME Terminal and xterm don't), each redraw is a 100 KB-1 MB PNG so it is slow over SSH, and headless Chrome takes hundreds of MB of RAM per instance.