fix(skill)!: reference pixel-point/animate-text — stop vendoring

Per James and Miguel's review feedback:
  James: "you can only reference the skill or recreate things"
  Miguel: "I'd just reference the skill without trying to copy
           everything"
  James: "we can't vendor their artifacts in our own repo"

The 48 vendored text-effects JSON files were direct copies from
pixel-point/animate-text (verified: typewriter.json matches the
upstream byte-for-byte at duration_ms: 240, stagger_ms: 46,
easing: steps(1, end)). That repo has no LICENSE file, so the
files default to "all rights reserved" — Apache 2.0 redistribution
in our repo is a compliance violation.

The earlier "rewrite from scratch" attempt produced JSON that
didn't render correctly (7 of 24 effects broke when I built a demo
HTML to validate them). Rather than keep iterating on a rewrite
that doesn't match the upstream's calibration, this commit drops
the vendored files entirely and updates skill prose to REFERENCE
the upstream skill instead.

### Changes

- Delete `skills/hyperframes/assets/text-effects/` (48 JSON files
  + the dual-directory structure, 8451 lines).
- Rewrite `skills/hyperframes/references/text-effects.md` as a
  reference page that:
  - Names pixel-point/animate-text as the source of truth
  - Explains why we don't ship the catalog (licensing gap)
  - Tells sub-agents to load `/animate-text` via Claude Code skill
    invocation or `npx skills add pixel-point/animate-text`
  - Lists the 24 effect IDs by category as vocabulary (so agents
    can name effects in STORYBOARD.md before loading the upstream)
  - Documents the fallback path: implement from name + GSAP
    knowledge if the upstream skill isn't available
- Update 5 cross-references to reframe the catalog as upstream-
  referenced instead of repo-bundled:
  - skills/hyperframes/references/techniques.md (TOC pointer)
  - skills/hyperframes/references/beat-direction.md (text-anim
    guidance bullet)
  - skills/website-to-hyperframes/references/capabilities.md
    (registry-overview entry)
  - skills/website-to-hyperframes/references/step-3-storyboard.md
    (storyboard template + Text Animations section format)
  - skills/website-to-hyperframes/references/beat-builder-guide.md
    (references table row)

### What sub-agents see

Before: read `text-effects.md` → see 24 named effects → read each
spec from in-repo `assets/text-effects/effects/<id>.json`.

After: read `text-effects.md` → see 24 named IDs and a load
instruction → invoke `/animate-text` (or `npx skills add
pixel-point/animate-text`) → read each spec from
`.agents/skills/animate-text/assets/effects/<id>.json` (the
upstream's own files, not vendored copies).

End-user UX cost: one extra `npx skills add` for projects that
want the deterministic catalog. Or accept the fallback where
sub-agents implement from effect name + GSAP knowledge — works
fine for simple effects, less ideal for the 3 layout-aware ones
(kinetic-center-build, short-slide-right, short-slide-down).

Net diff on heygen-com#991: -8488 lines.

Author: ukimsanov