feat: port MaskedHeading animation from react-bits

[adetyaz]

Summary

• Ports MaskedHeading from react-bits (ts-tailwind variant) — a heading whose letters act as an SVG clip-path mask, revealing an image or video underneath, with idle drift, pointer parallax, and a staggered entrance animation (rise/wipe/fade, triggered on mount/view/hover).
• Preserves all props, defaults, and behavior 1:1 with upstream: word-by-word glyph positioning synced to real DOM layout on every resize/font-load, the same time-correct exponential smoothing for drift/parallax, and the same three-mode reveal animation via GSAP.
• Adds a full docs/demo page (selects for media/reveal/trigger/align, sliders for every numeric prop, prop table, code tab) plus the exact demo video asset used by react-bits' own preview.

Test plan

• svelte-check — no errors/warnings in the new files
• eslint — clean
• registry:build — jsrepo registry sync passes
• build — production build succeeds
• Verified in-browser via Playwright: glyph positions now match react-bits' rendering exactly (word wrap, x/y per glyph) after fixing a nbsp-escaping bug that was inflating word widths and breaking the wrap