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/Dockerfile

@@ -0,0 +1,30 @@
+FROM node:20-alpine AS base
+RUN corepack enable && corepack prepare pnpm@latest --activate
+
+FROM base AS deps
+WORKDIR /app
+COPY pnpm-workspace.yaml pnpm-lock.yaml package.json ./
+COPY apps/platform-dash/package.json ./apps/platform-dash/package.json
+RUN pnpm install --frozen-lockfile --filter @homelab/platform-dash...
+
+FROM base AS builder
+WORKDIR /app
+COPY --from=deps /app ./
+COPY apps/platform-dash ./apps/platform-dash
+RUN pnpm --filter @homelab/platform-dash build
+
+FROM base AS runner
+WORKDIR /app
+ENV NODE_ENV=production
+
+RUN addgroup --system --gid 1001 nodejs
+RUN adduser --system --uid 1001 nextjs
+
+COPY --from=builder /app/apps/platform-dash/public ./apps/platform-dash/public
+COPY --from=builder --chown=nextjs:nodejs /app/apps/platform-dash/.next/standalone ./
+COPY --from=builder --chown=nextjs:nodejs /app/apps/platform-dash/.next/static ./apps/platform-dash/.next/static
+
+USER nextjs
+EXPOSE 3200
+ENV PORT=3200
+CMD ["node", "apps/platform-dash/server.js"]