Bump express from 5.1.0 to 5.2.0 in /backend (#39)

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
...

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Author: dependabot[bot]

backend/package.json

@@ -15,7 +15,7 @@
       "date-fns": "4.1.0",
       "dayjs": "1.11.18",
       "dotenv": "16.4.5",
-      "express": "5.1.0",
+      "express": "5.2.0",
       "jsonwebtoken": "9.0.2"
     },
     "devDependencies": {