[umiyosh]

Summary

Adds the two checks #19 still asked for, text size and contrast, to motion-render check, and closes the gap in #23 where a stop shorter than 0.4 s was never reported.

Closes #23. Part of #19 (this completes its automated checks). Part of #16.

Changes

• scripts/snapshot.js (page side): for every element with text of its own, measures
  • the font size as drawn, including transforms (a heading scaled up by a push-in counts at its drawn size)
  • the WCAG contrast ratio of its color over its background, composited from the page down through its ancestors' backgrounds. Text drawn at opacity under 0.9 is skipped: it is dimmed on purpose or fading in or out. A gradient or image background, or a color space other than sRGB, gives no ratio rather than a guess.
• scripts/layout.ts: two new findings for still boxes, with the same two-samples-in-a-row rule as the others:
  • A is 20px, smaller than 24px
  • A has contrast 2.1:1, needs 4.5:1 (3:1 for text 40 px and up, following WCAG's lower bar for large text)
• checkLayout samples every 0.1 s instead of 0.2 s, so a pose held for 0.2 s is reported (check: a stop shorter than 0.4 s is not reported #23). A one-minute film takes about 8 s to check (was about 3 s).
• references/html-film.md: the new outputs and how to fix them (dark numbers on light badges; 24 px floor for sources and labels; faded text is not measured, so text meant to be read must not be faded).

What it found

• WIF film (wif-v4): the step-number badges in the numbered flow, white digits on light teal and blue, at 3.7:1 and 1.9:1. This is the same problem hyperframes check found in the Phase 0 spike. No false positives.
• A new film on catastrophic forgetting in fine-tuning, made end to end with this branch: layout: ok after one fix (a breathing chip sticking out of its dashed slot).

Test plan

• make check: lint, typecheck, format, knip, quality gate (no new violations)
• vitest run --coverage: 93 tests pass (layout.ts 100% lines)
• New tests: small and faint text are reported and large text has the lower bar (unit); in a page, an 18 px source, a faint line, and a chip resting 0.3 s on a card's text are all reported (the last one is missed at 0.2 s sampling)
• End to end on an account without Motion: narrate → bgm → kit → check → stills → sfx → build
• CI