feat(m1-2,m1-3): deterministic core + mask keying (TDD, green)
Card 2 (deterministic core) + Card 3 (capture+mask geometry):
- src/lib/core/math.js: scale, sqft, bdft, roundHalfUp, width sampling,
1/8-inch snap — implemented to docs/CAPTURE.md identities.
- src/lib/core/mask.js: keySheet green/black/auto chroma keys + maskStats.
- fixed sensitivity scale (0-100, higher = looser = keeps more)
- fixed inverted green threshold (150 - s)
- black key drops bright saturated sheets via saturation gate
- tests/unit/math.test.js: corrected 3 wrong expected values to match the
spec (sqft 21x12in = 1.75 not 17.5; bdft 3.06; sample avg 11.25).
- tests/e2e/mask.spec.js: skeleton, skipped pending M1-5 live UI.
Full unit suite green: 24/24. E2e collects clean.
Ty
dd011207a0