feat: scaffold center and guild backend NestJS skeletons

Fabric.Backend.Center/src/nodes/nodes.controller.ts

@@ -0,0 +1,24 @@
+import { Body, Controller, Get, Post } from '@nestjs/common';
+
+type NodeRegistration = {
+  nodeId?: string;
+  name?: string;
+  endpoint?: string;
+  handshakeProof?: string;
+};
+
+@Controller('nodes')
+export class NodesController {
+  private readonly nodes: NodeRegistration[] = [];
+
+  @Post('register')
+  register(@Body() body: NodeRegistration) {
+    this.nodes.push(body);
+    return { status: 'accepted', handshake: 'todo-verify-shared-secret', node: body };
+  }
+
+  @Get()
+  list() {
+    return { items: this.nodes };
+  }
+}