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

backend/socket/index.js

@@ -0,0 +1,61 @@
+const { Server } = require('socket.io');
+const { verifyToken } = require('../auth');
+const { getUserById } = require('../db');
+const { setupBoardRoom } = require('./board-room');
+
+/**
+ * Set up Socket.IO on the given HTTP server.
+ * Returns the io instance.
+ */
+function setupSocket(httpServer) {
+  const io = new Server(httpServer, {
+    cors: {
+      origin: process.env.CORS_ORIGIN || '*',
+      methods: ['GET', 'POST'],
+    },
+    pingInterval: 25000,
+    pingTimeout: 60000,
+  });
+
+  // JWT authentication middleware
+  io.use((socket, next) => {
+    try {
+      const token = socket.handshake.auth?.token;
+      if (!token) {
+        return next(new Error('Authentication required'));
+      }
+
+      const decoded = verifyToken(token);
+      const user = getUserById(decoded.id);
+      if (!user) {
+        return next(new Error('User not found'));
+      }
+
+      // Store user info on socket
+      socket.userId = user.id;
+      socket.userEmail = user.email;
+      socket.userDisplayName = user.display_name;
+      socket.userRole = user.role;
+
+      next();
+    } catch (err) {
+      next(new Error('Invalid token'));
+    }
+  });
+
+  // Handle connections
+  io.on('connection', (socket) => {
+    console.log(`[socket] User connected: ${socket.userDisplayName} (${socket.userId})`);
+
+    // Set up board room handlers
+    setupBoardRoom(io, socket);
+
+    socket.on('disconnect', (reason) => {
+      console.log(`[socket] User disconnected: ${socket.userDisplayName} (${reason})`);
+    });
+  });
+
+  return io;
+}
+
+module.exports = { setupSocket };