Enable GPU: LLM + Whisper on the RTX 5050, pick qwen3:8b

GPU acceleration is now on by default and verified end-to-end on the
Blackwell RTX 5050 (sm_120):

- Ollama offloads 100% to GPU (log: library=CUDA compute=12.0,
  BLACKWELL_NATIVE_FP4=1). compose passes GPU via CDI
  (devices: nvidia.com/gpu=all) to both ollama and javis.
- Whisper STT on GPU: faster-whisper>=1.1.0 + nvidia-cublas/cudnn cu12,
  LD_LIBRARY_PATH baked into the image. Verified float16 transcribe on
  sm_120; bridge auto-falls back to CPU when no GPU is present.
- Model: default chat model -> qwen3:8b (best 8GB-VRAM tool-calling,
  ~5GB Q4). Embed stays nomic-embed-text.
- README documents the host one-time setup (nvidia-container-toolkit +
  `nvidia-ctk cdi generate`) and GPU on/off.

Verified: image builds; GPU visible in both containers via compose;
ollama ps = 100% GPU; faster-whisper cuda OK + CPU fallback OK;
bridge /health 200.

bridge/server.py

@@ -90,7 +90,16 @@ def _ensure_brain():
             )
             device = os.environ.get("WHISPER_DEVICE", "auto")
             compute = os.environ.get("WHISPER_COMPUTE_TYPE", "auto")
-            whisper = WhisperModel(cfg.whisper_model, device=device, compute_type=compute)
+            try:
+                whisper = WhisperModel(cfg.whisper_model, device=device, compute_type=compute)
+            except Exception as ge:
+                # GPU not available / unsupported -> fall back to CPU so the
+                # bridge still works without a GPU passed to the container.
+                if device != "cpu":
+                    print(f"[bridge] whisper device='{device}' failed ({ge}); falling back to CPU", flush=True)
+                    whisper = WhisperModel(cfg.whisper_model, device="cpu", compute_type="int8")
+                else:
+                    raise
 
             _cfg, _db, _dialogue_memory, _whisper = cfg, db, dialogue_memory, whisper
             print(f"[bridge] brain ready (chat={cfg.ollama_chat_model}, whisper={cfg.whisper_model})", flush=True)