feat(studio): keyframe diamonds, navigation, context menu [4/6]

[miguel-heygen]

Summary

KeyframeDiamond toggle, KeyframeNavigation (◀ ◆ ▶), TimelineClipDiamonds with connecting lines, KeyframeDiamondContextMenu with ease picker.

Part 4 of 6 — UI components (new files only). Depends on PR 3.

Test plan

• Diamond markers appear on timeline clips
• Click diamond → seek + select
• Right-click → context menu with ease/delete/copy

[miguel-heygen]

Warning

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• feat(studio): runtime-synced design panel + 3D props + split polish #1188
• fix(studio): overlay jump, delete-all, split polish [9/10] #1191
• feat(studio): runtime-first dynamic keyframe system [8/10] #1190
• feat(studio): split clip at playhead for media elements [7/10] #1189
• feat(studio): design panel, timeline polish, feature flag [6/6] #1172
• feat(studio): keyframe hooks wiring — session, cache, toolbar [5/6] #1171
• feat(studio): keyframe diamonds, navigation, context menu [4/6] #1170 👈 (View in Graphite)
• feat(studio): GSAP runtime bridge + optimistic updates [3/6] #1169
• feat(core): spring physics solver + runtime fixes [2/6] #1168
• feat(core): GSAP keyframe parsing, mutations, and API routes [1/6] #1167
• main

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