feat(core): clip-model hf- ids minted at parse, emitted as data-hf-id (R1) (#1270)

* feat(core): clip-model hf- ids minted at parse, emitted as data-hf-id (R1)

* docs(core): document legacy-id round-trip in clip-model readback (R1 review)

Addresses Rames' review on #1270: clarifies that a pre-R1 clip authored with
id="my-title" round-trips as data-hf-id="my-title" (non-hf-shaped but stable,
exact-match) by design — targeting uses exact [data-hf-id="…"] match and does
not require the hf- shape; legacy values re-mint only at the R7 write-back. Not
a bug. Comment-only.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

* docs(core): fix misleading legacy-id migration comment in htmlParser.ts

The original comment said legacy data-hf-id values "are re-minted only
once the R7 write-back persists freshly-minted ids to source" — which is
incorrect. ensureHfIds skips elements that already carry data-hf-id, so
legacy values (e.g. data-hf-id="my-title") persist indefinitely and are
NOT automatically re-minted. Exact-match targeting still works correctly.
Update comment to reflect actual behaviour.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

* test(core): update htmlParser tests for R1 hf- id minting

Pre-R1 tests expected clip ids to reflect legacy `id=` attributes.
After R1, ensureHfIds runs first and mints data-hf-id — so clip.id
reflects the minted hf- value unless the element already has data-hf-id.

Fix: add explicit data-hf-id to test HTML elements where tests assert
specific id values. Update no-id test to expect hf- format (/^hf-[a-z0-9]{4}$/)
instead of the pre-R1 generated-id fallback (/^element-\d+$/).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

packages/core/src/generators/hyperframes.ts

@@ -447,6 +447,7 @@ function generateZoomGsapAnimations(
 function generateElementHtml(element: TimelineElement, keyframes?: Keyframe[]): string {
   const baseAttrs = [
     `id="${element.id}"`,
+    `data-hf-id="${element.id}"`,
     `data-start="${element.startTime}"`,
     `data-end="${element.startTime + element.duration}"`,
     `data-layer="${element.zIndex}"`,