feat(core): add GSAP keyframe + motion-path source mutations

[miguel-heygen]

Stack: GSAP keyframe + motion-path editing — core read/write layer (#1553 → #1561).

What

Add core parser + writer support for keyframe and motion-path source mutations on GSAP tweens: add / remove / update keyframes, convert a flat tween to keyframes, edit motion-path waypoints, and classify tween properties into groups (position / scale / rotation / visual).

Why

The Studio keyframe/motion-path editor needs deterministic, AST-level read and write of GSAP timelines so that edits round-trip through the composition source without reformatting unrelated code.

How

• Extend the Acorn-based GSAP writer (gsapWriterAcorn.ts) with keyframe/motion-path ops.
• Parser surfaces keyframes, property groups, and resolved tween timing (gsapParser.ts, gsapConstants.ts).
• Writer-vs-parser parity tests lock emitted source against what the parser reads back.

Test plan

• Unit tests added (parser + writer parity)
• bun run test (core) green

[miguel-heygen]

Warning

This pull request is not mergeable via GitHub because a downstack PR is open. Once all requirements are satisfied, merge this PR as a stack on Graphite.
Learn more

• feat(studio): keyframes flag, gesture recording + timeline/selection refinements #1561
• feat(studio): on-canvas motion-path overlay #1560
• feat(studio): motion-path geometry + commit helpers #1559
• feat(studio): GSAP drag/commit/bridge editing infra #1558
• feat(studio): GSAP runtime read layer + shared helpers #1557
• feat(cli): add keyframes command to surface motion paths #1556
• feat(core): route motion-path mutations through studio-api + fix clip stamping #1555
• feat(core): add GSAP keyframe + motion-path source mutations #1554 👈 (View in Graphite)
• chore(producer): shim __filename/__dirname in the CJS banner #1553
• main

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[jrusso1020]

Approved at c8aee055 per Rames D Jusso "stamp-ready with 1 nit + 1 question." Deferring his specific items (posted in his review) to Miguel for resolution inline — non-blocking from my side.

PR body is the unfilled template; please fill in even a one-paragraph description before merge so the change history names what landed (Rames D Jusso + Via both flagged this as a stack-wide process concern across all 9 PRs).

[terencecho]

Test-coverage + backwards-compat axis (complementary to @rames-jusso's structural pass)

Reviewed with a narrower lens: do the new mutation APIs ship with tests, and is anything signature-broken on the existing parser/writer surface?

Verified

• Test coverage strong on the new surface:
  • gsapParser.test.ts adds units for updateMotionPathPointInScript (4 cases), addMotionPathPointInScript (2 cases), removeMotionPathPointInScript (2 cases), addMotionPathToScript (1 case), syncPositionHoldsBeforeKeyframes (6 cases), addKeyframeToScript backfill on/off (2 cases), _auto exclusion (1 case).
  • gsapWriter.parity.test.ts adds removeKeyframeFromScript array-form parity (3 cases: implicit-% removal, collapse-on-fewer-than-2, no-op on mismatched %).
• Writer parity scope is correct. Motion-path mutations are intentionally recast-only (live in gsapParser.ts, no acorn counterpart) because #1555 routes them through studio-api (server-side). The browser/SDK acorn writer doesn't need them — the studio calls them via HTTP. So the parity test absence for motion-path is by design, not a gap.
• No export signature breaks: every export touched in gsapParser.ts and gsapWriterAcorn.ts is an ADDITION (verified by git diff filter on ^[-+]\s*export function — no - lines).

Note

• The commit message describes the surface well, but the PR body is the unfilled template — see consolidated note on #1561. For the most critical PR in the stack (+651/-4 core mutations), the empty body makes the change harder to justify to a future archaeologist.

— Review by tai (pr-review)