feat(auth): implement user authentication with JWT and NextAuth

- Added user registration and login functionality with JWT authentication.
- Created auth controller, service, and module in the backend.
- Implemented user model and user products management.
- Integrated NextAuth for session management on the frontend.
- Added middleware for protecting routes and handling public access.
- Updated frontend API routes to include authorization headers.
- Enhanced recipe and user product models to support ownership and visibility.
- Created registration and login pages in the frontend.
- Added necessary types for NextAuth session management.

backend/src/users/users.module.ts

@@ -0,0 +1,10 @@
+import { Module } from '@nestjs/common';
+import { UsersService } from './users.service';
+import { PrismaModule } from '../prisma/prisma.module';
+
+@Module({
+  imports: [PrismaModule],
+  providers: [UsersService],
+  exports: [UsersService],
+})
+export class UsersModule {}

backend/src/users/users.service.ts

@@ -0,0 +1,19 @@
+import { Injectable } from '@nestjs/common';
+import { PrismaService } from '../prisma/prisma.service';
+
+@Injectable()
+export class UsersService {
+  constructor(private readonly prisma: PrismaService) {}
+
+  findByUsername(username: string) {
+    return this.prisma.user.findUnique({ where: { username } });
+  }
+
+  findById(id: number) {
+    return this.prisma.user.findUnique({ where: { id } });
+  }
+
+  create(data: { username: string; email: string; passwordHash: string }) {
+    return this.prisma.user.create({ data });
+  }
+}