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.

src/kc/kc.controller.ts

@@ -0,0 +1,26 @@
+import { Body, Controller, Get, Post, UseGuards } from '@nestjs/common';
+import { AuthGuard } from '@nestjs/passport';
+import { KcService } from './kc.service';
+import { CreateKcDto } from './dto/create-kc.dto';
+import { Roles } from '../common/roles.decorator';
+import { RolesGuard } from '../common/roles.guard';
+import { Role } from '../common/role.enum';
+
+@Controller('kc')
+@UseGuards(AuthGuard('authentik'), RolesGuard)
+export class KcController {
+  constructor(private readonly kc: KcService) {}
+
+  /// Only the Leitungsteam may create new KC events.
+  @Post()
+  @Roles(Role.LEITUNGSTEAM)
+  create(@Body() dto: CreateKcDto) {
+    return this.kc.createKc(dto.name);
+  }
+
+  @Get()
+  @Roles(Role.LEITUNGSTEAM)
+  list() {
+    return this.kc.listKcs();
+  }
+}