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

backend/unified-api/src/middleware/request-context.js

@@ -0,0 +1,9 @@
+import { randomUUID } from 'node:crypto';
+
+export function requestContext(req, res, next) {
+  const incoming = req.get('X-Request-Id');
+  req.requestId = incoming || randomUUID();
+  res.setHeader('X-Request-Id', req.requestId);
+  res.locals.startedAt = Date.now();
+  next();
+}