Fix webhook listener to use alpine/k8s image with kubectl

- Switch from alpine:latest to alpine/k8s:1.28.13
- Ensures kubectl is available for job creation
- Webhook now successfully triggers build jobs

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

webhook-build-trigger.yaml

@@ -176,7 +176,7 @@ spec:
       serviceAccountName: build-trigger-sa
       containers:
       - name: listener
-        image: alpine:latest
+        image: alpine/k8s:1.28.13
         command:
         - sh
         - -c
@@ -192,7 +192,7 @@ spec:
               while read line; do
                 if echo "$line" | grep -q "POST /webhook"; then
                   echo "Webhook received! Triggering build..."
-                  /scripts/trigger-build.sh &
+                  bash /scripts/trigger-build.sh &
                   break
                 fi
               done