add NestJS skeleton and GET /api/health-check.

Thin API bootstrap with config module and nullcart-style health route for Docker checks.

backend/src/config/index.ts

@@ -0,0 +1,22 @@
+import { registerAs } from '@nestjs/config';
+import { AppConfig } from '../types/AppConfig';
+import { NodeEnv } from '../types/NodeEnv';
+
+const env = (key: string): string => process.env[key] || '';
+
+const envInt = (key: string): number => parseInt(env(key), 10);
+
+export const getAppConfig = (): AppConfig => {
+    const rawOrigins = env('CORS_ORIGINS');
+
+    return {
+        port: envInt('BACKEND_PORT'),
+        nodeEnv: env('NODE_ENV') as NodeEnv,
+        corsOrigins: rawOrigins
+            .split(',')
+            .map(o => o.trim())
+            .filter(Boolean)
+    };
+};
+
+export default registerAs('app', getAppConfig);