Add platform-dash: S3 artifact browser for Garage object store

Lightweight Next.js app for browsing, uploading, and downloading
artifacts from the cluster-local Garage S3 bucket. Uses the harness
design system. Features:
- File/folder browser with breadcrumb navigation
- Drag-and-drop upload
- Download and delete
- Ingress at platform.coreworlds.io (internal-only)

Also adds platform-dash to CI/deploy workflows.

apps/platform-dash/k8s/base/service.yaml

@@ -0,0 +1,15 @@
+apiVersion: v1
+kind: Service
+metadata:
+  name: platform-dash
+  namespace: apps
+  labels:
+    app: platform-dash
+spec:
+  type: ClusterIP
+  ports:
+    - port: 80
+      targetPort: 3200
+      protocol: TCP
+  selector:
+    app: platform-dash