P2: Backend name requires exact string — no aliases for vitis/dml

[Shreyas582]

Description

--backend vitis fails with "backend not found". The user must pass the exact internal name --backend "AMD Vitis NPU". Similarly, --backend directml works but --backend dml does not.

This is poor UX — users should be able to use short aliases.

Reproduction

wraithrun --live --backend vitis --model ... --task ssh-keys
# Error: backend not found

wraithrun --live --backend "AMD Vitis NPU" --model ... --task ssh-keys
# Works

Expected Behavior

Accept common aliases:

• vitis / npu → AMD Vitis NPU
• dml / directml / gpu → DirectML
• cpu → CPU (already works)

Affected Files

• inference_bridge/src/onnx_vitis.rs or inference_bridge/src/lib.rs (backend name resolution)