Slice 14b — Wire beat grid detection into editor shell

[cbaucom]

Summary

• Auto-detect BPM from the selected soundtrack via decodeMono + detectBeatGrid
• Pass effective beat grid (manualBeatGrid ?? beatGridCache) into plan() so image slide durations snap to beats
• Persist beatGridCache and manualBeatGrid in slideshow.json
• Settings panel: Beat sync toggle + Energy (calm/medium/punchy)
• Soundtrack panel: BPM status line, tap tempo, manual BPM/offset entry

Closes #34

Acceptance criteria

• Soundtrack loaded → BPM detection runs and grid passed to plan()
• beatSync: true (default) snaps slide boundaries; off uses exact durations
• Energy + Beat sync controls in GlobalSettingsPanel
• Manual BPM (tap + numeric) stored as manualBeatGrid, survives reopen
• Loaded manualBeatGrid wins over re-detection

Test plan

• pnpm test, pnpm lint, pnpm build
• Open project with soundtrack → see "Analyzing…" then "NNN BPM · detected · syncing to beat"
• Toggle Beat sync off → status updates; slide durations match image duration setting
• Tap along (8 taps) or Apply manual BPM → "manual" in status; reopen project → persists
• Switch energy calm/punchy → total runtime shifts

Made with Cursor

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