Build(deps): Bump the uv group across 1 directory with 2 updates (#212)

Bumps the uv group with 2 updates in the /backend directory: [unstructured](https://github.com/Unstructured-IO/unstructured) and [protobuf](https://github.com/protocolbuffers/protobuf).


Updates `unstructured` from 0.18.13 to 0.18.18
- [Release notes](https://github.com/Unstructured-IO/unstructured/releases)
- [Changelog](https://github.com/Unstructured-IO/unstructured/blob/main/CHANGELOG.md)
- [Commits](Unstructured-IO/unstructured@0.18.13...0.18.18)

Updates `protobuf` from 6.33.0 to 6.33.5
- [Release notes](https://github.com/protocolbuffers/protobuf/releases)
- [Commits](https://github.com/protocolbuffers/protobuf/commits)

---
updated-dependencies:
- dependency-name: unstructured
  dependency-version: 0.18.18
  dependency-type: direct:production
  dependency-group: uv
- dependency-name: protobuf
  dependency-version: 6.33.5
  dependency-type: indirect
  dependency-group: uv
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

backend/pyproject.toml

@@ -40,7 +40,7 @@ dependencies = [
     "sphinxcontrib-mermaid==1.0.0",
     "sqlalchemy>=2.0.43",
     "starlette>=0.49.1",
-    "unstructured==0.18.13",
+    "unstructured==0.18.18",
 ]
 
 [dependency-groups]