HTML5 WebP capture + Google Font auto-registration on export

[dazzatronus]

Summary

• HTML5 clips capture frames as WebP instead of PNG (~30ms vs ~1s/frame), bake in bounded concurrent batches so the editor stays responsive, and show a bottom-edge "Loading video…" indicator while baking.
• Removed the dead Html5Player duration-detection logic — frame count now bakes the full clip uniformly.
• getEdit()/export auto-registers catalogued Google Fonts a clip references into timeline.fonts, so an edit built without an explicit add_font still renders with the correct font instead of falling back or failing.

Test plan

• tsc + build clean; jest 1785/1785 pass (incl. new tests/font-autoregister.test.ts)
• Render rich-text using a Google Font with no fonts[] entry → correct font in output
• HTML5 clip bakes without freezing the editor; loading indicator shows; animation plays the full clip

Note

SDK now requires canvas ≥ 2.8.2 (calls computeHtml5FrameCount without detectedDurationMs). Dependency is currently ^2.8.0 — bump the floor to ^2.8.2 before merge.