Bump langchain from 0.3.25 to 0.3.27 in /backend

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.3.25 to 0.3.27.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.3.25...langchain==0.3.27)

---
updated-dependencies:
- dependency-name: langchain
  dependency-version: 0.3.27
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

backend/requirements.txt

@@ -12,7 +12,7 @@ google_auth_oauthlib==1.2.2
 google-cloud-core==2.4.3
 json-repair==0.39.1
 pip-install==1.3.5
-langchain==0.3.25
+langchain==0.3.27
 langchain-aws==0.2.25
 langchain-anthropic==0.3.15
 langchain-fireworks==0.3.0