[v0.1.15] 2026-03-06

- Updated helios-core to v1.3.65

## Radiation Model
- Added Vulkan compute backend, enabling GPU ray tracing on AMD, Intel, and Apple Silicon GPUs without CUDA/OptiX
- Radiation plugin now supported on macOS via Vulkan (MoltenVK)
- Build system updated to compile and package SPIR-V shaders alongside PTX files
- Wheel builds on macOS now include radiation and energybalance plugins with bundled MoltenVK runtime

## Build & Packaging
- Dropped Python 3.8 support; added Python 3.12 and 3.13
- CI Vulkan SDK installation step added for macOS wheel builds
- Library loader auto-configures `VK_ICD_FILENAMES` for bundled MoltenVK on macOS

## Testing
- Excluded `tests/manual/` directory from automatic pytest collection
- Fixed visualizer headless detection on macOS (skip unless `PYHELIOS_TEST_VISUALIZER` is set)

Author: bnbailey-psl