build(deps): bump express from 5.1.0 to 5.2.0 in /backend

Bumps [express](https://github.com/expressjs/express) from 5.1.0 to 5.2.0.
- [Release notes](https://github.com/expressjs/express/releases)
- [Changelog](https://github.com/expressjs/express/blob/master/History.md)
- [Commits](expressjs/express@v5.1.0...v5.2.0)

---
updated-dependencies:
- dependency-name: express
  dependency-version: 5.2.0
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

backend/package.json

@@ -40,7 +40,7 @@
     "date-fns": "3.6.0",
     "dotenv": "16.4.5",
     "etag": "1.8.1",
-    "express": "5.1.0",
+    "express": "5.2.0",
     "express-rate-limit": "7.5.1",
     "firebase-admin": "12.0.0",
     "helmet": "4.6.0",