Fix half-speed playback and audio echo on slower machines

[dazzatronus]

What

Preview playback now follows real wall-clock time. The playhead previously advanced by accumulating per-frame deltas that were capped to a 60fps budget, so on any machine that could not sustain 60fps it advanced slower than real time: video ran at roughly half speed, and audio (which plays at real time on its own hardware clock) was repeatedly re-synced backwards onto the lagging playhead, producing an echo. One cause, both symptoms.

Behaviour change

• Playback tracks real elapsed time on every machine. On slow hardware visual frames drop instead of the clock slowing down; audio and video stay in sync.
• Export is unaffected: it sets the playhead to each exact frame time and remains deterministic.

How

play() anchors performance.now() and the current playback time; each tick sets playbackTime = anchor + (now - anchorWall). The per-frame audio/video re-sync logic becomes a rare safety net rather than a continuous correction loop. Removed the PixiJS ticker.minFPS = 60 line that was capping the frame-time delta.

Verify

DevTools → Performance → CPU throttle (6× or 20×), then play a timeline with audio: a 10s clip takes 10s of real time and audio stays in sync; only the visual frame rate drops. jest is green (1802 tests).

Note for reviewers: a pre-existing typecheck failure unrelated to this change (asset src optionality) is addressed separately; this PR touches only the playback clock.

[github-actions]

🎉 This PR is included in version 2.11.7 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀