refactor(native): split drawing internals

[markm39]

Summary

• move recognized-shape path building, hold recognition, snapping, and shape transform helpers into cpp/ShapeRecognition
• move shared native drawing structs/history deltas into cpp/DrawingTypes and delta apply/revert helpers into cpp/DrawingHistory
• move Stroke::ensureEraserCacheValid out of the shared drawing-type header and into cpp/DrawingTypes.cpp
• split crayon and calligraphy path-renderer implementations into cpp/PathRendererCrayon.cpp and cpp/PathRendererCalligraphy.cpp, leaving shared variable-width/spline logic in cpp/PathRenderer.cpp
• split SkiaDrawingEngine operations into focused C++ translation units for selection, eraser, and rendering/export behavior while keeping the engine API unchanged
• update helper headers to depend on drawing types instead of the full engine header
• include the root package version fix in the example lockfile and keep the native smoke compile linked against the new C++ module

Validation

• npm run validate
• clang++ -std=c++20 -fsyntax-only cpp/*.cpp -I cpp -I node_modules/@shopify/react-native-skia/cpp/skia -I node_modules/@shopify/react-native-skia/cpp/skia/modules/pathops/include
• npm audit --audit-level=moderate
• npm --prefix example audit --audit-level=moderate fails with the existing Expo/PostCSS moderate advisory; confirmed the same failure on main
• simplify review: no findings
• security review: no findings in changed native/package code; example audit advisory remains pre-existing

No device/app run performed per request.