fix(metrics): wire training pod scraping to Grafana dashboard

Three root causes for "no metrics" on the training dashboard:

1. Dashboard template variables ($model, $fold) sourced from
   foxhunt_training_current_epoch which isn't emitted until the first
   epoch completes. Switch to foxhunt_training_step which fires from
   step 500 onward.

2. train.sh pod template missing Prometheus annotations
   (prometheus.io/scrape, port, path). Also add the
   app.kubernetes.io/component label to the eval manifest so
   evaluation pods are discoverable too.

3. DQN and PPO trainers only called set_epoch() at the END of each
   epoch. Move the call to the TOP of the epoch loop so the gauge
   exists from the first training iteration.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

infra/scripts/train.sh

@@ -196,6 +196,10 @@ spec:
         foxhunt/job-type: training
         foxhunt/model: ${model}
         foxhunt/preset: ${PRESET}
+      annotations:
+        prometheus.io/scrape: "true"
+        prometheus.io/port: "9094"
+        prometheus.io/path: "/metrics"
     spec:
       restartPolicy: Never
       nodeSelector:
@@ -341,7 +345,12 @@ spec:
     metadata:
       labels:
         app.kubernetes.io/part-of: foxhunt
+        app.kubernetes.io/component: training-workflow
         foxhunt/job-type: evaluate
+      annotations:
+        prometheus.io/scrape: "true"
+        prometheus.io/port: "9094"
+        prometheus.io/path: "/metrics"
     spec:
       restartPolicy: Never
       nodeSelector: