fix(argo): alpha-rl reads predecoded from feature-cache PVC

The MBP-10 predecoded sidecars live on feature-cache-pvc at
/feature-cache/predecoded/, not on training-data-pvc. Points
--predecoded-dir to the correct PVC mount.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

infra/k8s/argo/train-multi-seed-template.yaml

@@ -518,7 +518,7 @@ spec:
             if [ "$MODEL" = "alpha-rl" ]; then
               stdbuf -oL $NSYS_PREFIX ${BINARY} \
                 --mbp10-data-dir /data/futures-baseline-mbp10/{{workflow.parameters.symbol}} \
-                --predecoded-dir /data/futures-baseline-mbp10/{{workflow.parameters.symbol}} \
+                --predecoded-dir /feature-cache/predecoded \
                 --out /workspace/output \
                 --n-steps 50000 \
                 --n-backtests 16 \