refactor: migrate to ES modules

package.json type=module, tsconfig module/moduleResolution=NodeNext,
target es2022, explicit .js on all relative imports. Center: jsonwebtoken
& bcryptjs switched to default imports (ESM/CJS interop). Verified:
builds, boots, full auth + plugin round-trip work under ESM.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/health.integration.spec.ts

@@ -18,7 +18,7 @@ describe('center integration (mysql + api)', () => {
   let app: INestApplication;
 
   beforeAll(async () => {
-    const { AppModule } = await import('./app.module');
+    const { AppModule } = await import('./app.module.js');
     const moduleRef = await Test.createTestingModule({
       imports: [AppModule],
     }).compile();