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/package.json

@@ -0,0 +1,21 @@
+{
+  "name": "refboard-backend",
+  "version": "1.0.0",
+  "description": "RefBoard — collaborative reference board backend",
+  "main": "server.js",
+  "scripts": {
+    "start": "node server.js"
+  },
+  "dependencies": {
+    "bcryptjs": "^2.4.3",
+    "better-sqlite3": "^11.7.0",
+    "cors": "^2.8.5",
+    "express": "^4.21.1",
+    "jsonwebtoken": "^9.0.2",
+    "minio": "^8.0.2",
+    "multer": "^1.4.5-lts.1",
+    "sharp": "^0.33.2",
+    "socket.io": "^4.8.1",
+    "uuid": "^11.0.3"
+  }
+}