feat: initialize backend with NestJS, PostgreSQL, and Prisma

- Add package.json for backend dependencies and scripts.
- Create Prisma schema for multi-tenant event management.
- Implement main application module and configure global settings.
- Develop authentication module with JWT and Authentik integration.
- Create DTOs for guest account creation and KC management.
- Implement role-based access control with custom guards and decorators.
- Add services and controllers for managing KCs and guest accounts.
- Set up global validation and CORS in the main application entry point.
- Establish Prisma module for database access throughout the application.
- Document project plan and architecture for multi-tenant platform.

backend/src/kc/kc.service.ts

@@ -0,0 +1,18 @@
+import { Injectable } from '@nestjs/common';
+import { randomBytes } from 'crypto';
+import { PrismaClient } from '../prisma/prisma.module';
+
+@Injectable()
+export class KcService {
+  constructor(private readonly prisma: PrismaClient) {}
+
+  createKc(name: string) {
+    return this.prisma.kc.create({
+      data: { name, inviteCode: randomBytes(6).toString('hex') },
+    });
+  }
+
+  listKcs() {
+    return this.prisma.kc.findMany();
+  }
+}