feat: scaffold center and guild backend NestJS skeletons

Fabric.Backend.Guild/src/channels/channels.controller.ts

@@ -0,0 +1,9 @@
+import { Body, Controller, Post } from '@nestjs/common';
+
+@Controller('channels')
+export class ChannelsController {
+  @Post()
+  create(@Body() body: Record<string, unknown>) {
+    return { status: 'todo', action: 'create-channel', received: body };
+  }
+}