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/auth/decorators/current-user.decorator.ts

@@ -0,0 +1,8 @@
+import { createParamDecorator, ExecutionContext } from '@nestjs/common';
+
+export const CurrentUser = createParamDecorator(
+  (_data: unknown, ctx: ExecutionContext) => {
+    const request = ctx.switchToHttp().getRequest();
+    return request.user as { userId: number; username: string };
+  },
+);

backend/src/auth/decorators/public.decorator.ts

@@ -0,0 +1,4 @@
+import { SetMetadata } from '@nestjs/common';
+
+export const IS_PUBLIC_KEY = 'isPublic';
+export const Public = () => SetMetadata(IS_PUBLIC_KEY, true);