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

frontend/src/socket.ts

@@ -0,0 +1,46 @@
+import { io, Socket } from 'socket.io-client';
+import { getToken } from './auth';
+
+let socket: Socket | null = null;
+
+export function getSocket(): Socket | null {
+  return socket;
+}
+
+export function connectSocket(): Socket {
+  if (socket?.connected) {
+    return socket;
+  }
+
+  const token = getToken();
+  socket = io(window.location.origin, {
+    auth: { token },
+    transports: ['websocket', 'polling'],
+    reconnection: true,
+    reconnectionAttempts: 10,
+    reconnectionDelay: 1000,
+  });
+
+  socket.on('connect', () => {
+    console.log('[socket] connected:', socket?.id);
+  });
+
+  socket.on('disconnect', (reason) => {
+    console.log('[socket] disconnected:', reason);
+  });
+
+  socket.on('connect_error', (err) => {
+    console.error('[socket] connection error:', err.message);
+  });
+
+  return socket;
+}
+
+export function disconnectSocket(): void {
+  if (socket) {
+    socket.disconnect();
+    socket = null;
+  }
+}
+
+export { Socket };