cuda_available() only covers "no GPU present". On a shared card the GPU
can exist but fail to load the model (VRAM exhausted by another process
e.g. Ollama). Try CUDA first, fall back to a CPU model on any load
error instead of crashing the transcription job. Supports HA portability
(node without GPU) and a contended GPU. Adds GPU-path + fallback tests.
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
