v0.3.0 — three templates, one engine

Three templates instead of one, running the same engine.

Added

• scaffold --template <name>. next is still the default; astro and
  html are new, and --template with no name lists them. The project records
  which one it came from, so later frames and --diff runs need no flag, and
  scaffolding a different template over an existing project is refused rather
  than leaving a tree that is neither.

• An Astro template. Ships no framework JavaScript, only the engine.

• A zero-build HTML template. No package.json, no tsconfig, no bundler,
  nothing to install. It does need a real HTTP server: module scripts and web
  workers are same-origin only, so file:// will not work. Its story outline is
  regenerated from components/story.js by frames, between markers in
  index.html — edit the story, not the markup.

Changed

• The scrubbing runtime moved into lib/, shared by every template. A fix
  to the decode window, the easing or the scrim is now one change rather than
  one per template. ScrollSequence.tsx went from 687 lines to about 135: the
  engine owns the canvas, worker, decode window, animation frame, listeners,
  reduced motion and the copy overlays, and the adapter hands it a container.

• The engine ships its own stylesheet, keyed off data attributes and
  themeable through custom properties (--st-beat-heading-size,
  --st-scrim-falloff, and the rest). Restyling a beat no longer means editing
  markup you no longer own. It also takes the story outline, which was
  previously hidden by a Tailwind utility — so a template without Tailwind gets
  the same behaviour.

• The frames contract and the story are now JavaScript with types beside
  them — frames.js + frames.d.ts, story.js + story.d.ts. A page with
  no build step cannot import TypeScript, and those are exactly the files it has
  to import. Editors and builds still check them: the templates that have a type
  checker turn on checkJs, so a mistyped align still fails.

  Existing projects: re-run scrollytelling scaffold . to pick up the new
  files. It never overwrites anything you have edited, and
  scrollytelling scaffold . --diff reports what moved. Your story.ts keeps
  working until you switch; the generated contract is what changes name.

Fixed

• A page whose opening frames all decoded could report "no frames found".
  The opening request covers the whole decode window, but only about half of
  those are opening frames, and readiness counted every failure so far.

• Web workers were not emitted by every bundler. The engine constructed its
  worker indirectly, and bundlers detect only the literal
  new Worker(new URL(..., import.meta.url)) form. Turbopack traced it anyway;
  Vite did not, so an Astro build shipped no worker and fell back to
  main-thread decoding with only a console warning.