Add crisp zoom rendering

[markm39]

Summary

• Adds zoom-aware native render viewport props from JS through iOS, Android, and the shared Skia engine.
• Renders completed strokes through scale-bucketed tiles so settled zoom stays crisp without re-rendering the whole path set each frame.
• Keeps high-zoom performance bounded with native render-scale budgeting, tile cache invalidation, and an iOS drawable-size recursion fix.

Test plan

• Manual iPad dev-build validation during implementation: drawing coordinates stayed accurate through zoom in/out, settled strokes rendered crisp, and the final lag profile was acceptable for shipping.
• npm run validate
• Full C++ render syntax check: clang++ -std=c++20 -fsyntax-only cpp/SkiaDrawingEngine.cpp cpp/SkiaDrawingEngineRendering.cpp cpp/SkiaDrawingEngineEraser.cpp cpp/SkiaDrawingEngineSelection.cpp cpp/ActiveStrokeRenderer.cpp cpp/PathRenderer.cpp cpp/PathRendererCrayon.cpp cpp/PathRendererCalligraphy.cpp cpp/DrawingTypes.cpp cpp/DrawingHistory.cpp cpp/DrawingSelection.cpp cpp/BackgroundRenderer.cpp cpp/DrawingSerialization.cpp cpp/ShapeRecognition.cpp cpp/EraserRenderer.cpp cpp/StrokeSplitter.cpp cpp/BatchExporter.cpp -I cpp -I node_modules/@shopify/react-native-skia/cpp/skia -I node_modules/@shopify/react-native-skia/cpp/skia/modules/pathops/include
• git diff --check
• Simplify review gate: no required changes.
• Security review gate: no credential, authz, injection, or sensitive-data findings.