perf(transform): translate-only fast path for global transforms

[chiefcll]

Summary

Three fixes covering the hot update path for x/y changes on simple nodes (no rotation/scale/mount). Targets CoreNode.update and Matrix3d.

• update Global block (🐛 [BUG] - CanvasTextRenderer tints color-emoji glyphs with node.color, crushing native emoji colors #1, big win): when both the node is isSimple and the parent's global is translate-only, the resulting global is also translate-only and collapses to two adds on tx/ty. Bypasses the 6-field Matrix3d.copy + 2 mul-add translate. Tracked with a per-node _globalIsTranslate flag that propagates down the tree. RTT chains conservatively opt out.
• updateLocalTransform simple path ([fix] [sdf] Sdf text alpha double multiplication #2): localTransform is guaranteed identity-shape (ta=1, tb=0, tc=0, td=1), so only tx/ty need to change between frames — skips 4 redundant field writes. _localIsTranslate tracks identity-shape so a non-simple → simple transition correctly restores the matrix.
• updateBoundingRect ([fix] [subtexture] Update quad on subtexture node texture set #5, correctness bug): fix || → && on the axis-aligned-fast-path check. With ||, a matrix with one zero shear component and the other non-zero (e.g. tb=0, tc=-0.5) wrongly took the diagonal fast path and produced incorrect bounds. Now matches calculateRenderCoords semantics.

Adds a setTranslate(x, y) helper on Matrix3d for the in-place tx/ty + mutation-flag write used by both the local and global fast paths.

Test plan

• pnpm test — 120/120 passing
• pnpm build — clean
• Lint (prettier + eslint) clean on changed files
• 12 new unit tests for setTranslate, simple-path reuse, non-simple → simple transitions, translate-only propagation through grandchildren, fast-path opt-out, and the bounding-rect axis check
• Visual regression — recommend running locally before merge; no shader/rendering math changed but bounds change is observable for sheared matrices

🤖 Generated with Claude Code