Bump langgraph from 0.6.11 to 1.0.1 in /backend (#2680)

Bumps [langgraph](https://github.com/langchain-ai/langgraph) from 0.6.11 to 1.0.1.
- [Release notes](https://github.com/langchain-ai/langgraph/releases)
- [Commits](langchain-ai/langgraph@0.6.11...1.0.1)

---
updated-dependencies:
- dependency-name: langgraph
  dependency-version: 1.0.1
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]