feat(api): add unified v2 gateway and mobile read slice

backend/unified-api/src/app.js

@@ -0,0 +1,31 @@
+import express from 'express';
+import pino from 'pino';
+import pinoHttp from 'pino-http';
+import { requestContext } from './middleware/request-context.js';
+import { errorHandler, notFoundHandler } from './middleware/error-handler.js';
+import { healthRouter } from './routes/health.js';
+import { createAuthRouter } from './routes/auth.js';
+import { createProxyRouter } from './routes/proxy.js';
+
+const logger = pino({ level: process.env.LOG_LEVEL || 'info' });
+
+export function createApp(options = {}) {
+  const app = express();
+
+  app.use(requestContext);
+  app.use(
+    pinoHttp({
+      logger,
+      customProps: (req) => ({ requestId: req.requestId }),
+    })
+  );
+
+  app.use(healthRouter);
+  app.use('/auth', createAuthRouter({ fetchImpl: options.fetchImpl, authService: options.authService }));
+  app.use(createProxyRouter(options));
+
+  app.use(notFoundHandler);
+  app.use(errorHandler);
+
+  return app;
+}