runtime: preserve semantic states and bound repair work

[rwang23]

Summary

• preserve native semantic error, warning, success, diff, link, disabled, focus, selection, reduced-motion, and forced-colors behavior while keeping Full Skin structural surfaces
• scope runtime repair to route/runtime-relevant child-list mutations, add a health-check fallback for target replacement, and enforce a long-session mutation budget
• record runtime evidence separately from captured v2 assets so the Gallery and Theme Manager label v3 as source-tested and recapture-required rather than current app proof

Verification

• npm run check
• npm run test:source
• npm run test:generated
• npm run runtime:benchmark (10,000 unrelated mutations; zero repair/ensure calls)
• isolated browser checks for Gallery evidence labeling in Chinese and English, plus light/dark semantic-state computed colors

Remaining release evidence

• fresh v3 capture on the named ChatGPT Beta test bench
• isolated Stable/Beta CDP smoke after the runtime update
• physical Windows/macOS comparison of the fixed background before changing its attachment strategy

Refs #14

[rwang23]

Superseded by #26, now merged into main at e2ed6e8. This branch head is already included in main; closing the draft avoids duplicate review and merge work.