Fix build trigger container image to use Alpine-based image

- Switch from bitnami/kubectl to alpine/k8s for proper package manager
- Add curl to dependencies for potential future webhook support

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

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

build-trigger-cronjob.yaml

@@ -139,12 +139,12 @@ spec:
           restartPolicy: Never
           containers:
           - name: trigger
-            image: bitnami/kubectl:latest
+            image: alpine/k8s:1.28.13
             command: ["/bin/bash"]
             args:
             - -c
             - |
-              apk add --no-cache git bash
+              apk add --no-cache git bash curl
               /scripts/trigger-build.sh
             volumeMounts:
             - name: script