Bump starlette from 0.48.0 to 0.52.1 in /back-end

Bumps [starlette](https://github.com/Kludex/starlette) from 0.48.0 to 0.52.1.
- [Release notes](https://github.com/Kludex/starlette/releases)
- [Changelog](https://github.com/Kludex/starlette/blob/main/docs/release-notes.md)
- [Commits](Kludex/starlette@0.48.0...0.52.1)

---
updated-dependencies:
- dependency-name: starlette
  dependency-version: 0.52.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

back-end/requirements.txt

@@ -12,7 +12,7 @@ pydantic==2.12.5
 python-multipart==0.0.22
 six==1.17.0
 sniffio==1.3.1
-starlette==0.48.0
+starlette==0.52.1
 typing_extensions==4.15.0
 uvicorn==0.41.0
 pytest==9.0.2