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/next.config.js

@@ -0,0 +1,5 @@
+/** @type {import('next').NextConfig} */
+const nextConfig = {
+  output: "standalone",
+};
+module.exports = nextConfig;