record-demo: VHS demo GIFs for mcpc

The tapes in docs/vhs/*.tape are VHS scripts that drive a real shell session — VHS types each command, runs it against a live MCP server, captures the terminal, and renders a GIF. The README hero is docs/images/mcpc-demo.gif, built from docs/vhs/mcpc-demo.tape.

This file is the accumulated know-how. Read all of it before touching a tape — most rules below were discovered by hitting the wall, and skipping them wastes whole render cycles (~1–2 min each).