feat: Add Z Anti-Aliasing (ZAA) non-planar contouring support

Port of ZAA from BambuStudio-ZAA (github.com/adob/BambuStudio-ZAA)
to stock BambuStudio. ZAA eliminates stair-stepping on curved surfaces
by raycasting each extrusion point against the mesh and adjusting
Z height to follow the true surface geometry.

Changes:
- Core algorithm: ContourZ.cpp (~330 lines) performs vertical raycasting
- 3D geometry: Point3, Line3, Polyline3, MultiPoint3 extensions
- ExtrusionPath::polyline changed from Polyline to Polyline3
- GCode writer emits per-point Z when path.z_contoured is set
- Pipeline step posContouring in PrintObject after perimeter/infill gen
- 5 new print settings under Quality (zaa_enabled, zaa_min_z, etc.)
- GUI integration: config options, preset registration, search support
- Guard for missing resources/nonplanar/ directory
- cmake_minimum_required bumped to 3.5 for CMake 4.x compatibility
- Build script, build guide, and release guide for macOS