[api] Bump litestar from 2.15.1 to 2.15.2 in /backend

Bumps [litestar](https://github.com/litestar-org/litestar) from 2.15.1 to 2.15.2.
- [Release notes](https://github.com/litestar-org/litestar/releases)
- [Commits](litestar-org/litestar@v2.15.1...v2.15.2)

---
updated-dependencies:
- dependency-name: litestar
  dependency-version: 2.15.2
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

backend/poetry.lock

@@ -13,7 +13,7 @@ readme = "../README.md"
 
 [tool.poetry.dependencies]
 python = "^3.12"
-litestar = {extras = ["prometheus"], version = "^2.15.1"}
+litestar = {extras = ["prometheus"], version = "^2.15.2"}
 gunicorn = "23.0.0"
 pydantic = "^2.11.3"
 uvicorn = {extras = ["standard"], version = "^0.34.0"}