infra: add feature-cache-pvc (persistent fxcache storage)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

infra/k8s/argo/feature-cache-pvc.yaml

@@ -0,0 +1,18 @@
+# Dedicated PVC for precomputed .fxcache files.
+# Survives workflow completions (unlike workspace volumeClaimTemplate).
+# Precompute writes here, all training steps read from here.
+apiVersion: v1
+kind: PersistentVolumeClaim
+metadata:
+  name: feature-cache-pvc
+  namespace: foxhunt
+  labels:
+    app.kubernetes.io/name: feature-cache
+    app.kubernetes.io/part-of: foxhunt
+spec:
+  accessModes:
+    - ReadWriteOnce
+  storageClassName: scw-bssd-retain
+  resources:
+    requests:
+      storage: 10Gi