Recording clips / video download & format conversion #30

Explicitly a v1 non-goal (PLAN.md §1), and structurally off today: the FFmpeg build disables all muxers and encoders (build/scripts/build-ffmpeg.sh — --disable-encoders --disable-muxers), so there is no output/write path at all.

Filed to track the post-v1 decision. Cheapest viable shape: remux-only (no re-encode) clip capture / stream download, which needs muxers (not encoders) re-enabled plus a packet-tap off the demux stage. Full format conversion (re-encode) is a much bigger lift and likely stays out of scope.