docs(motion): point authors at the official HyperFrames agent skills

The vendor publishes seek-safe authoring doctrine as installable agent
skills (hyperframes-keyframes / hyperframes-creative / hyperframes-core);
its primary seek-safe primitive is GSAP tweens on window.__timelines —
the kit's CSS register is a house pattern and the clip-window rule is
its empirically-derived companion.

motion/README.md

@@ -44,6 +44,7 @@ A panel-demo clip is a FILM of software being used, not a screenshot with captio
 - **A cursor that doesn't behave like a hand.** Drive it with `data-waypoints`: it fades in, travels with eased legs, rests with an idle sway (kit adds this), clicks with a visible cause→effect (the click precedes the thing it triggers), and leaves the frame — it never pops in, freezes pixel-still, or blinks out mid-scene.
 - **A metronome.** Identical beat lengths with identical flat entrances read as a slideshow. Vary entrance energy (the kit cards take a springy overshoot well), let a beat breathe after a click, and give the climax (stats/receipt) a different rhythm than the build.
 - **Verify motion, not stills.** After `request_render`, sample PAIRS of frames ~0.5s apart around each cursor/camera beat and compare positions — a single frame proves presence, only a pair proves movement.
+- **The vendor ships agent skills for this.** HyperFrames publishes official authoring skills (`npx skills add heygen-com/hyperframes --skill hyperframes-keyframes` for seek-safe keyframe rules across runtimes, `hyperframes-creative` for beat planning, `hyperframes-core` for the composition contract; router skill `/hyperframes`). Consult them before authoring a new register. Note the vendor's primary seek-safe animation primitive is GSAP tweens registered on `window.__timelines` — this kit's CSS-animation register is a house pattern, and the clip-window rule below is its empirically-derived seek-safety companion.
 - **Clip windows are for structural layers only.** The renderer's per-clip visibility scheduler drifts badly behind the encoded timeline on long compositions (measured live: a 40s cut whose per-beat clips only reached the ~19s mark by the final frame — the entire tail silently missing from the MP4). Give `class="clip"` + `data-start`/`data-duration` only to full-length structural layers (the cold-open, the panel frame), and drive every BEAT inside them with the kit's pattern instead: base-hidden styles (`opacity: 0`) plus a delayed CSS animation (`animation-delay` + `forwards`/`both` fill) — those run on the correct clock. If a beat must also disappear, give it an exit animation, not a clip window.
 
 ## Panel-demo kit (`kit/`)