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/App.tsx

@@ -0,0 +1,51 @@
+import React from 'react';
+import { BrowserRouter, Routes, Route, Navigate } from 'react-router-dom';
+import { AuthProvider, useAuth } from './auth';
+import Login from './pages/Login';
+import CollectionList from './pages/CollectionList';
+import CollectionDetail from './pages/CollectionDetail';
+import Editor from './pages/Editor';
+
+function ProtectedRoute({ children }: { children: React.ReactNode }) {
+  const { user, loading } = useAuth();
+
+  if (loading) {
+    return (
+      <div style={{
+        display: 'flex', alignItems: 'center', justifyContent: 'center',
+        height: '100vh', background: '#1a1a1a', color: '#e0e0e0', fontSize: '18px',
+      }}>
+        Loading...
+      </div>
+    );
+  }
+
+  if (!user) {
+    return <Navigate to="/login" replace />;
+  }
+
+  return <>{children}</>;
+}
+
+function AppRoutes() {
+  return (
+    <Routes>
+      <Route path="/login" element={<Login />} />
+      <Route path="/" element={<ProtectedRoute><CollectionList /></ProtectedRoute>} />
+      <Route path="/collection/:collectionId" element={<ProtectedRoute><CollectionDetail /></ProtectedRoute>} />
+      <Route path="/board/:boardId" element={<ProtectedRoute><Editor /></ProtectedRoute>} />
+      <Route path="/c/:shareToken" element={<CollectionDetail isPublicView />} />
+      <Route path="*" element={<Navigate to="/" replace />} />
+    </Routes>
+  );
+}
+
+export default function App() {
+  return (
+    <BrowserRouter>
+      <AuthProvider>
+        <AppRoutes />
+      </AuthProvider>
+    </BrowserRouter>
+  );
+}