fix: train-dqn params aligned with compile-and-train (commit-sha + git-branch)

Was using commit-ref which doesn't exist in compile-and-train template.
Now passes commit-sha=HEAD + git-branch=main matching the parent template.

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

infra/k8s/argo/train-dqn-template.yaml

@@ -32,7 +32,9 @@ spec:
     parameters:
       - name: model
         value: dqn
-      - name: commit-ref
+      - name: commit-sha
+        value: HEAD
+      - name: git-branch
         value: main
       - name: gpu-pool
         value: ci-training-h100