Add authentication system and admin panel

- Implement JWT-based authentication with login/logout
- Add user management routes and middleware
- Create admin panel for managing words and categories
- Add authentication store and API client
- Update database schema with User model
- Configure CORS and authentication middleware
- Add login page and protected routes

packages/backend/prisma/schema.prisma

@@ -8,17 +8,25 @@ generator client {
 datasource db {
   provider = "mysql"
   url      = env("DATABASE_URL")
+  shadowDatabaseUrl = env("SHADOW_DATABASE_URL")
 }
 
 // ============================================
 // AUTHENTICATION & USERS
 // ============================================
 
+enum UserRole {
+  ADMIN
+  USER
+}
+
 model User {
   id            String    @id @default(uuid())
   email         String    @unique
   displayName   String?   @map("display_name")
   passwordHash  String?   @map("password_hash")
+  role          UserRole  @default(USER)
+  isActive      Boolean   @default(true) @map("is_active")
   authProvider  String    @default("local") @map("auth_provider") // local, google, microsoft
   providerId    String?   @map("provider_id")
   createdAt     DateTime  @default(now()) @map("created_at")