perf(transform): scale-only path, eager allocation, contain cache

[chiefcll]

Summary

Stacked on top of #13. Follow-ups to the translate-only fast path:

• fix: eliminate props divergence between CoreNode and CoreTextNode #3 — scale-only branch + Matrix3d.rotate(0) guard: Matrix3d.rotate now skips Math.cos(0)/Math.sin(0) (neither V8 nor JSC constant-folds them) and writes an identity directly. updateLocalTransform splits the rotation/scale logic into three branches — rotation (full multiply path), scale-only (4-mul in-place .scale()), and translate-only. Avoids building a separate scaleRotate matrix and collapses the 8-mul multiply to 4 muls for the common UI-animation case of scale without rotation.
• chore: remove dead orphaned textures management #6 — eager allocation + stop reassigning: CoreNode now allocates localTransform and globalTransform as identity matrices in the constructor. The Global block reuses these instances via Matrix3d.copy(src, dst) instead of reassigning the field, keeping the field's hidden class stable. Dead parent.globalTransform || lt and if (gt === undefined) fallbacks are removed. _localIsTranslate now defaults to true since the eagerly-allocated matrix is already identity-shape, so the very first update takes the fast path. Stage root init copies in place into the eagerly-allocated globalTransform.
• fix: bake node color into canvas texture to preserve emoji colors #4 — cached _hasContainResize: updateIsSimple computes the boolean once when texture/textureOptions change; updateLocalTransform reads the flag instead of running the optional-chain + string compare on every Local update.

Test plan

• pnpm test — 132/132 passing
• pnpm build — clean
• Lint (prettier + eslint) clean on changed files
• 12 new unit tests covering Matrix3d.rotate(0) identity output and reset semantics, scale-only path output (ta/td set, tb/tc untouched) including pivot algebra, constructor-time matrix allocation and instance reuse across simple/non-simple frames, and _hasContainResize flag transitions
• Visual regression — recommend running locally before merge

Note: base branch is #13. Rebase onto main once #13 lands.

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