refactor(studio): split oversized files to pass 600-line check

[miguel-heygen]

Summary

• 7 Studio files exceeded the 600-line CI limit after the keyframe system was merged
• Extracted logical chunks into new modules: helper functions, sub-components, sub-hooks
• No behavior changes — pure code organization

Files split

File	Before	After	Extracted to
App.tsx	747	578	useGestureCommit.ts, useBlockHandlers.ts
PropertyPanel.tsx	682	557	propertyPanel3dTransform.tsx, helpers in propertyPanelHelpers.ts
gsapRuntimeBridge.ts	647	281	gsapDragCommit.ts, gsapRuntimeReaders.ts
useDomEditSession.ts	643	577	useDomEditPreviewSync.ts
useGsapScriptCommits.ts	640	567	gsapKeyframeCacheHelpers.ts
useTimelineEditing.ts	617	495	timelineEditingHelpers.ts
manualEditsDom.ts	611	563	gsapAnimatesProperty.ts

Test plan

• All 7 target files are under 600 lines
• tsc --noEmit passes clean