Extract shared hook timing utilities

[natashaannn]

Closes #18

Summary

• Consolidated hookClipEnd() into a single remotion/lib/hookTiming.ts — previously four separate implementations in SegmentPlayer, CameraPlayer, HookOverlay, and Composition could disagree by 1–3 frames per hook, causing hooks to cut early or extend too far on some renders.
• Extracted getHookSubClips() and buildHookSections() into the shared lib so all hook-section builders use identical logic; de-overlap pass moved here too.
• SegmentPlayer re-exports SubClip and Section for backward compatibility — no changes required in any downstream consumer.
• Added 21 unit tests covering bounded/unbounded hooks, token-tail extension, next-hook bridging, de-overlap, and Whisper marker filtering.

How to review

• remotion/lib/hookTiming.ts — new canonical implementation; verify the bounded vs unbounded logic, tail pad constants, and bridge condition match the intent in CLAUDE.md (constants: HOOK_TAIL_PAD_UNBOUNDED_SECONDS=0.16, HOOK_TAIL_PAD_BOUNDED_SECONDS=0.02, HOOK_BRIDGE_MAX_GAP_SECONDS=1.0).
• remotion/lib/hookTiming.test.ts — 21 tests; confirm edge cases (Whisper markers, bridging, overlap) are covered and assertions are not trivially true.
• remotion/components/SegmentPlayer.tsx — diff should show only: deletion of local getHookSubClips + buildSections hook logic, addition of buildHookSections import, re-export of SubClip/Section types.
• remotion/components/CameraPlayer.tsx — diff should show only: deletion of local hook branch in getOutputDuration, addition of hookClipEnd import.
• remotion/components/HookOverlay.tsx — diff should show only: deletion of local buildHookTimings implementation, addition of hookClipEnd import.
• remotion/Composition.tsx / remotion/ShortFormClip.tsx — each now imports from hookTiming.ts rather than duplicating the calculation inline.

Test plan

• npm test passes — 14 suites, 207 tests, 0 failures
• React and node Jest projects both green
• 3 Playwright E2E smoke tests pass
• Frame parity confirmed — hookClipEnd produces identical results to pre-refactor SegmentPlayer implementation for all hook segment shapes (verified against live transcript data)
• Remotion Studio visual check — hook clip boundaries correct, camera switches at hook boundaries work

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