fix(studio): soft-reload GSAP property edits, preserve shader cache (#1129)

* fix(studio): soft-reload GSAP property edits without iframe reload

GSAP property value edits (opacity, x, scale, etc.) now update the live
timeline inside the preview iframe without triggering a full iframe
reload. This preserves the WebGL context and shader transition cache,
eliminating the loading overlay that appeared on every property edit.

Implementation:
- New gsapSoftReload.ts: kills the old GSAP timeline, re-executes the
  updated script, calls __hfForceTimelineRebind(), and re-seeks to the
  current time. Falls back to full reload on failure.
- useGsapScriptCommits: passes softReload: true for property value edits
  via the existing (previously unused) softReload flag on commitMutation.
- hyper-shader.ts: exposes __hfSuppressSceneMutations on the window so
  the soft-reload can suppress the MutationObserver during re-execution.
- hyper-shader.ts: getDocumentScriptSignature now excludes pure GSAP
  animation scripts from the cache key hash, so full reloads (undo,
  external changes) don't invalidate transition caches when only
  animation values changed.

* fix(studio): wrap soft-reload script in IIFE to avoid const redeclaration

The new script ran in the same global scope as the old one, causing
Identifier tl has already been declared errors from const/let
re-declarations. Wrapping in an IIFE creates a new lexical scope.
Also remove the old script element before inserting the new one.

* fix(studio): return scriptText from mutation API, drop client-side HTML parsing

The mutation API already has the extracted GSAP script text (newScript)
after rewriting. Return it as scriptText in the response so
applySoftReload receives the script directly instead of parsing HTML
client-side. This avoids DOMParser compatibility issues across test
environments and is more reliable than regex-based extraction.

* fix(studio): align soft-reload script heuristic with server-side parser

The client's findGsapScriptElement only matched gsap.timeline and
__timelines. The server's extractGsapScriptBlock also matches .to( and
.set(. Aligned the client heuristic to prevent silent fallback to full
reload for compositions that use tl.to() without gsap.timeline in the
same script.

* fix(studio): address hf#1129 review — multi-script guard, scope docs

- Return false (fallback to full reload) when multiple GSAP scripts
  exist in the document, since it's ambiguous which one to replace
- Add docstring scoping the optimization to root-document scripts
  (template-wrapped sub-compositions fall back to full reload)
- Add code comment explaining the IIFE scope constraint
- Add test for the multi-script guard

* fix(studio): align cache key filter with soft-reload script heuristic

isGsapAnimationOnlyScript now also matches .to( and .set( patterns,
matching findGsapScriptElement. Scripts using only tl.to() without
gsap.timeline were excluded from soft-reload but still busted the
shader cache on full-reload paths (undo, external changes).