Bump langchain from 0.2.10 to 0.3.0 in /src/backend

Bumps [langchain](https://github.com/langchain-ai/langchain) from 0.2.10 to 0.3.0.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain==0.2.10...langchain==0.3.0)

---
updated-dependencies:
- dependency-name: langchain
  dependency-type: direct:production
...

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

Author: dependabot[bot]

src/backend/requirements.txt

@@ -21,7 +21,7 @@ Werkzeug==3.0.3
 faiss-cpu==1.7.4
 pypdf==3.17.0
 pypdf2==3.0.1
-langchain==0.2.10
+langchain==0.3.0
 anthropic==0.2.10
 tika==2.6.0
 bs4==0.0.1