fix(playground): wait for browser error reports

[devallibus]

Summary

• add browser sync waiters for screenshot uploads and error reports in the playground DB layer
• make /api/playground/:sessionId/update resolve on actual browser feedback instead of idling on the screenshot timeout
• cover the new wait behavior with timing-aware node tests for failure and success flows

Verification

• bun run test:web
• manual local repro with a browser-connected playground session returns invalid GLSL compile errors in ~96ms instead of waiting ~5s

Closes #71.
Supersedes closed PR #73 after restacking onto current development.