v0.2.9

Release v0.2.9 - Fix GPU/CUDA Backend Loading

Fixes:
- GPU/CUDA now works correctly in installed builds
- Explicit backend loading via ggml_backend_load_all_from_path()
- NuGet CUDA12's stub ggml-cpu.dll replaced with full avx2 version
- Improved diagnostics for LLM initialization failures

This release fixes the issue where installed builds would fall back
to pre-canned emails instead of using GPU-accelerated LLM generation.