[cbaucom]

Closes #17

Summary

• Pure sequence-planner/playback helpers map playhead frames ↔ slide IDs from the RenderPlan
• Filmstrip shows a green "now playing" ring synced via requestAnimationFrame polling; click seeks to that slide and opens settings
• Present mode portals the player to document.body, requests fullscreen, hides editor chrome; Esc exits

Acceptance criteria

• Grid click jumps playback to slide start; playhead movement highlights current slide (green ring)
• Fullscreen/present mode shows only the rendered show; Esc exits
• Scrubbing uses Remotion Player + SlideshowComposition driven by RenderPlan (no separate render path)

Code review

Score: 4/5 — APPROVE

Frame→slide logic correctly lives in the pure module; editor shell stays thin. No determinism concerns. Tests cover slideIdAtFrame / startFrameForSlideId golden cases.

Non-blocking follow-ups: rAF poll runs while paused (fine at editor scale); slideIdAtFrame uses start-frame semantics so crossfade overlap may briefly highlight the incoming slide before it visually dominates; presentation mode remounts the player (playback state preserved via initialFrame).

Test plan

• pnpm test
• pnpm build
• pnpm lint
• Manual: play/scrub — green ring tracks; click thumb — seeks + settings modal; Present — chrome hidden, Esc exits
• node scripts/playwright-issue-17-smoke.mjs (requires dev server)

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