fix(sdk,studio): R5 cutover review fixes (on top of #1539) (#1545)

* fix(sdk,studio): R5 cutover review fixes — fromTo dest, timing sync, parity

Confirmed correctness findings from the R5 review of the SDK cutover stack,
applied on top of #1539:

- fromTo add via cutover dropped its destination: handleAddGsapTween read only
  `toProperties`; now falls back to `properties` like every other method.
- handleSetTiming GSAP sync: a clip with no data-start skipped the shift (now
  treats start as 0, matching the server path) and a blank/non-numeric
  data-start wrote position: NaN (now sanitized).
- handleSetTiming no longer appends an absolute position to an auto-sequenced
  (implicit-position) tween, which collapsed staggers.
- handleSetTiming keeps data-end in sync when a clip carries BOTH data-duration
  and data-end (a stale data-end inverted the clip).
- string/relative tween positions ("+=0.5", "<") documented as a known ceiling.
- opacity/autoAlpha property seed no longer falsy-zero (`|| 1`): an element at
  opacity 0 seeds 0, not 1.
- optimistic add-keyframe cache tolerance aligned to the writer's PCT_TOLERANCE
  (2%) so a near-neighbour keyframe no longer shows then vanishes on reload.
- DOM-patch finiteness validation runs before the SDK cutover path.
- attribute ops mapping to a reserved data-* name decline the cutover up front
  instead of throwing inside dispatch.

Regression tests added for each SDK-side fix.

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

* fix(studio): close two gaps in the reserved-attr cutover gate

- Lowercase the mapped attribute name before the reserved check, matching the
  SDK's validateSetAttribute (which lowercases), so a case-variant reserved
  name is declined up front instead of throwing inside dispatch.
- Also gate `html-attribute` ops (raw, non-prefixed names), not just bare
  `attribute` ops. Both the emitter and the gate now derive the name via one
  shared `sdkAttrName` helper so they can't drift.

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

* fix(studio): match keyframe remove-path tolerance to the writer (mirror of add)

The optimistic remove-keyframe cache filtered with `> 0.001`, dropping only a
near-exact match, while the writer removes within PCT_TOLERANCE (2). Removing
at e.g. 49% dropped a 50% keyframe on disk but left it in the cache — a phantom
that vanished on reload, the inverted twin of the add-path tolerance fix.
Now filters with `> 2` to match.

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

---------

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

packages/studio/src/hooks/useGsapKeyframeOps.ts

@@ -80,8 +80,12 @@ export function useGsapKeyframeOps({
         // appending a duplicate — matches addKeyframeToScript, which writes one
         // keyframe per percentage (merging properties).
         apply: (prev) => {
+          // Match addKeyframeToScript's merge tolerance (PCT_TOLERANCE = 2 in
+          // gsapWriterAcorn): a keyframe added within 2% of an existing one
+          // merges on disk, so the optimistic cache must merge it too — else the
+          // UI shows a phantom keyframe that vanishes on the next reload.
           const idx = prev.keyframes.findIndex(
-            (kf) => Math.abs((kf.tweenPercentage ?? kf.percentage) - percentage) < 0.001,
+            (kf) => Math.abs((kf.tweenPercentage ?? kf.percentage) - percentage) <= 2,
           );
           if (idx >= 0) {
             const keyframes = prev.keyframes.slice();
@@ -164,8 +168,13 @@ export function useGsapKeyframeOps({
         elementId: selection.id,
         apply: (prev) => ({
           ...prev,
+          // Match the writer's removal tolerance (PCT_TOLERANCE = 2 in
+          // gsapWriterAcorn): removing at e.g. 49% drops a keyframe at 50% on
+          // disk, so the optimistic cache must drop it too — else the stranded
+          // entry is a phantom that vanishes on the next reload (mirror of the
+          // add-path tolerance fix).
           keyframes: prev.keyframes.filter(
-            (kf) => Math.abs((kf.tweenPercentage ?? kf.percentage) - percentage) > 0.001,
+            (kf) => Math.abs((kf.tweenPercentage ?? kf.percentage) - percentage) > 2,
           ),
         }),
         persist: async () => {