v2.2 — honest speed readout + press kit

• The status bar after a reply now shows generation speed and prompt reading separately: 9 tok @ 5.10 t/s (read 61 in 11.8s). It used to divide the reply's tokens by the whole wait, including re-reading the chat history (one forward per prompt token), which showed e.g. 0.66 t/s.
• Landing-page README with a demo video, screenshots and a press kit (docs/media); build and training notes moved to docs/DEVELOPING.md.
• tools/sim: host screen simulator that runs the real firmware UI + model at device speed and regenerates all media; tools/video: Remotion promo.