Bump loguru from 0.7.2 to 0.7.3 in /backend

Bumps [loguru](https://github.com/Delgan/loguru) from 0.7.2 to 0.7.3.
- [Release notes](https://github.com/Delgan/loguru/releases)
- [Changelog](https://github.com/Delgan/loguru/blob/master/CHANGELOG.rst)
- [Commits](Delgan/loguru@0.7.2...0.7.3)

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

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

backend/pyproject.toml

@@ -19,7 +19,7 @@ dependencies = [
     "langchain==0.3.13",
     "langchain-openai==0.2.11",
     "langgraph==0.2.60",
-    "loguru==0.7.2",
+    "loguru==0.7.3",
     "orjson==3.10.12",
     "pwdlib[argon2]==0.2.1",
     "pydantic[email]==2.10.4",