Bump nltk from 3.10.0 to 3.10.3 in /src/backend

Bumps [nltk](https://github.com/nltk/nltk) from 3.10.0 to 3.10.3.
- [Release notes](https://github.com/nltk/nltk/releases)
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](nltk/nltk@v3.10.0...v3.10.3)

---
updated-dependencies:
- dependency-name: nltk
  dependency-version: 3.10.3
  dependency-type: direct:production
...

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

Author: dependabot[bot]

src/backend/pyproject.toml

@@ -67,7 +67,7 @@ dependencies = [
     "cryptography==50.0.0",
     "aiohttp==3.14.3",
     "pyasn1==0.6.4",
-    "nltk==3.10.0",
+    "nltk==3.10.3",
 ]
 
 [[tool.uv.index]]