feat(registry): add pendulum-swing component

[rottenpen]

What

Add a new registry component, pendulum-swing: a motion primitive that hangs content from a fixed pivot and lets it settle with a damped oscillation, like a hanging sign coming to rest on its hook.

Why

The catalog has plenty of "arrive" primitives (slam, pop, slide, dissolve) but none that reads as a physical hanging object settling. pendulum-swing fills that gap with a small, composable primitive that pins a top edge and swings the content in.

How

• Recipe-only snippet. pendulum-swing.html owns no timeline. It reads its variables, writes CSS custom props, and rotates about a transform-origin pinned to the pivot. All motion rides a single unitless custom property --hf-swing-angle that the host timeline eases 1 → 0, so only transform: rotate() animates — sub-pixel, no layout/reflow property, safe under the seek-by-frame capture engine.
• Damped-oscillation ease. The demo drives the swing with 1 - exp(-2.3·p)·cos(3.5π·p) — a cosine (the swings) inside an exponential decay (the damping), normalised so the tween lands exactly upright. The sign passes through center several times, each pass smaller, before resting — a real pendulum settle rather than a single overshoot.
• Four enum variables: pivot (top-center/left/right), amplitude (gentle/standard/wide), direction (right/left), tone (ink/paper/accent — each a bg/fg pair to keep AA contrast on any frame). Unrecognised overrides fall back to declared defaults.
• Component manifest carries no dimensions/duration (per schema). The demo carries the same variable declaration as the snippet.

Preview

The sign swings right → left → right, each pass smaller, settling upright.

pendulum-swing.mp4

Test plan

• npx hyperframes lint + npx hyperframes validate on both HTML files — clean (only ignore-level root_missing_* rules fire on the bare snippet, expected)
• Demo validates 0 errors / 0 warnings
• snippet == demo variable declaration parity verified
• registry.json regenerated via scripts/generate-registry-items.ts (not hand-edited); catalogArtifact.revision untouched
• Docs regenerated via scripts/generate-catalog-pages.ts (mdx + catalog-index.json + docs.json nav)
• Rendered the demo locally via the demo's own GSAP timeline to confirm the motion
• Unit tests — n/a (registry data + HTML, no package code changed)

Notes for maintainers (the two contributor-can't-finish steps)

Per CONTRIBUTING.md, these need assets an outside contributor isn't expected to install; neither blocks review:

1. Search index (registry/catalog-artifact/local-vectors.*) — not regenerated here (needs the 32 MB on-device embedding model). The Catalog: search index covers the registry CI job will name the gap; it's a deterministic rebuild from this registry, so it's regenerated before merge. Until then the item is findable by word search, just not by meaning.
2. Catalog preview image/MP4 — preview.poster in the manifest points at the conventional CDN path (static.heygen.ai/.../catalog/components/pendulum-swing.png); the actual asset is published by scripts/upload-docs-images.sh (HeyGen AWS creds), so a maintainer runs the official preview + upload before merge. The MP4 above is a local render for review.