phase 0+1: project scaffold + xserv-cuda crate

- Cargo workspace with xserv-cuda crate
- CUDA FFI bindings (cudart: memory, stream, device, error)
- GpuBuffer RAII wrapper with H2D/D2H/D2D copy
- CudaStream wrapper with RAII Drop
- CachingAllocator with size-bucketed free lists
- PinnedBuffer for page-locked host memory
- Device info query via cudaDeviceGetAttribute
- Vector-add CUDA kernel smoke test
- Integration test suite (11 tests)
- build.rs: cc crate compiles .cu for SM 12.0
- sync-and-build.sh for remote build on dash5
- Roadmap doc (docs/00-roadmap.md) and Phase 0+1 design doc

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

crates/xserv-cuda/src/lib.rs

@@ -0,0 +1,12 @@
+pub mod allocator;
+pub mod device;
+pub mod error;
+pub mod ffi;
+pub mod memory;
+pub mod stream;
+
+pub use allocator::CachingAllocator;
+pub use device::DeviceInfo;
+pub use error::{CudaError, Result};
+pub use memory::{GpuBuffer, PinnedBuffer};
+pub use stream::CudaStream;