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/auth.ts

@@ -0,0 +1,85 @@
+import React, { createContext, useContext, useState, useEffect, useCallback, ReactNode } from 'react';
+import { getMe } from './api';
+
+const TOKEN_KEY = 'refboard_token';
+
+export function getToken(): string | null {
+  return localStorage.getItem(TOKEN_KEY);
+}
+
+export function setToken(token: string): void {
+  localStorage.setItem(TOKEN_KEY, token);
+}
+
+export function removeToken(): void {
+  localStorage.removeItem(TOKEN_KEY);
+}
+
+export function isAuthenticated(): boolean {
+  return !!getToken();
+}
+
+export interface User {
+  id: string;
+  email: string;
+  username: string;
+  display_name: string;
+  role: string;
+}
+
+interface AuthContextType {
+  user: User | null;
+  loading: boolean;
+  login: (token: string, user: User) => void;
+  logout: () => void;
+}
+
+export const AuthContext = createContext<AuthContextType>({
+  user: null,
+  loading: true,
+  login: () => {},
+  logout: () => {},
+});
+
+export function useAuth(): AuthContextType {
+  return useContext(AuthContext);
+}
+
+export function AuthProvider({ children }: { children: ReactNode }) {
+  const [user, setUser] = useState<User | null>(null);
+  const [loading, setLoading] = useState(true);
+
+  useEffect(() => {
+    const token = getToken();
+    if (token) {
+      getMe()
+        .then((res) => {
+          setUser(res.data.user || res.data);
+        })
+        .catch(() => {
+          removeToken();
+        })
+        .finally(() => {
+          setLoading(false);
+        });
+    } else {
+      setLoading(false);
+    }
+  }, []);
+
+  const login = useCallback((token: string, userData: User) => {
+    setToken(token);
+    setUser(userData);
+  }, []);
+
+  const logout = useCallback(() => {
+    removeToken();
+    setUser(null);
+  }, []);
+
+  return React.createElement(
+    AuthContext.Provider,
+    { value: { user, loading, login, logout } },
+    children
+  );
+}