Profile large documents and refresh late font/style changes #12

P2 follow-up; not an automatic gate for the first stable release.

• Benchmark large and frequently changing documents; report node counts, timing and memory evidence.
• Decide bounded/incremental observation strategy from measurements.
• Design attribute/font-load refresh without self-triggered loops or redundant full-page writes.
• Add host/browser regressions for late fonts, changed classes/styles and cleanup.

Acceptance: measured improvement and a documented refresh contract; preserve existing host styles and provider-owned lifetime.

References: roadmap, development/acceptance guide.