fix(surface): preserve settled iframe heights

[benvinegar]

Summary

• defer suppressed rapid resize flips through a trailing re-measure instead of dropping them
• keep oscillating iframe heights settled on the taller value to avoid clipping
• add late safety measurements and font-ready reporting for slow async content
• expand BRIDGE_JS VM regression coverage for oscillation, A→B→A reflows, stale state, and late growth

Validation

• node --test test/surfacePage.test.ts
• npm test
• npm run typecheck
• npm run lint
• npm run format:check

This PR description was generated by Pi using OpenAI GPT-5 Codex