Refactor authentication system with tier-based access control

- Replace group-based auth with user/board/admin tier system
- Add direct login functionality alongside OAuth
- Implement role-based middleware for route protection
- Create dashboard pages and admin API endpoints
- Add error handling page and improved user management
- Maintain backward compatibility with legacy role methods

middleware/auth-admin.ts

@@ -0,0 +1,14 @@
+export default defineNuxtRouteMiddleware((to, from) => {
+  const { isAuthenticated, isAdmin } = useAuth();
+  
+  if (!isAuthenticated.value) {
+    return navigateTo('/login');
+  }
+  
+  if (!isAdmin.value) {
+    throw createError({
+      statusCode: 403,
+      statusMessage: 'Access denied. Administrator privileges required.'
+    });
+  }
+});

middleware/auth-board.ts

@@ -0,0 +1,14 @@
+export default defineNuxtRouteMiddleware((to, from) => {
+  const { isAuthenticated, isBoard, isAdmin } = useAuth();
+  
+  if (!isAuthenticated.value) {
+    return navigateTo('/login');
+  }
+  
+  if (!isBoard.value && !isAdmin.value) {
+    throw createError({
+      statusCode: 403,
+      statusMessage: 'Access denied. Board membership required.'
+    });
+  }
+});

middleware/auth-user.ts

@@ -0,0 +1,7 @@
+export default defineNuxtRouteMiddleware((to, from) => {
+  const { isAuthenticated } = useAuth();
+  
+  if (!isAuthenticated.value) {
+    return navigateTo('/login');
+  }
+});