Add the hosted MCP demo recording

The OpenAI app directory requires a Demo Recording URL, and it has to be a
URL we control and can keep alive for as long as the listing exists — so it
is served from here rather than from a video host that may expire it.

3:04 of the hosted server answering in ChatGPT: one call per tool, ending
with get_doc refusing an off-site URL, which is the safety behaviour the
review asks to see demonstrated. H.264, no audio, faststart so it can be
scrubbed without downloading the whole file; 10.8 MB of screen capture
re-encoded to 3.0 MB with the text still legible.

Author: Mikhus