Fix test config: don't treat CPU backend loading as failure

The failure pattern 'CPU backend' was incorrectly flagging the normal log
message 'load_backend: loaded CPU backend from...' as an error. This is
expected behavior - both CUDA and CPU backends are loaded, but GPU is
actually used for computation (as shown by 'offloaded 35/35 layers to GPU').

Changed failure patterns to detect actual GPU failures:
- Removed: 'CPU backend' (too broad, catches normal backend loading)
- Added: 'failed to load.*CUDA' (actual load failures)
- Added: 'no GPU detected' (GPU not available)

Root cause: monitor.go processes failure patterns first (highest priority),
so the 'CPU backend' pattern was creating EventError events before success
patterns could be checked, causing tests to fail despite GPU working.

test/config/quick.yaml

@@ -22,7 +22,8 @@ validation:
     failure:
       - "CUDA.*error"
       - "out of memory"
-      - "CPU backend"
+      - "failed to load.*CUDA"
+      - "no GPU detected"
 
 server:
   host: "localhost"