feat: RefBoard v0.4.0 — collaborative reference board with layers, groups & polished UI

Full-featured PureRef-style collaborative canvas for game dev teams:
- Layer panel with visibility, lock, drag reorder, group/ungroup (Ctrl+G/Shift+G)
- Arrangement tools (grid, row, column) via right-click context menu
- Copy to system clipboard (Ctrl+C writes PNG for external paste in Paint etc.)
- Number shortcuts (1-5) for tool selection with visible shortcut badges
- Premium dark UI across all pages (Login, Collections, Boards, Editor)
- Socket.IO rooms for cursors, transforms, and presence notifications
- MinIO image storage with backend proxy, drag/drop and paste upload

Dockerfile

@@ -0,0 +1,35 @@
+FROM node:20-alpine AS frontend-build
+WORKDIR /build
+COPY frontend/package.json ./frontend/
+RUN cd frontend && npm install
+COPY frontend/ ./frontend/
+RUN cd frontend && npm run build
+
+FROM node:20-alpine
+WORKDIR /app
+
+# Build tools for native modules (better-sqlite3, sharp)
+RUN apk add --no-cache python3 make g++
+
+# Backend dependencies
+COPY backend/package.json ./backend/
+RUN cd backend && npm install --production
+
+# Remove build tools to keep image smaller
+RUN apk del python3 make g++
+
+# Backend source
+COPY backend/ ./backend/
+
+# Frontend build output
+COPY --from=frontend-build /build/frontend/dist ./frontend/dist
+
+# Data directory for SQLite
+RUN mkdir -p /app/data
+
+# Health check utility
+RUN apk add --no-cache wget
+
+EXPOSE 8000
+
+CMD ["node", "backend/server.js"]