build(deps): bump langchain-core from 0.3.39 to 0.3.40 in /api

Bumps [langchain-core](https://github.com/langchain-ai/langchain) from 0.3.39 to 0.3.40.
- [Release notes](https://github.com/langchain-ai/langchain/releases)
- [Commits](langchain-ai/langchain@langchain-core==0.3.39...langchain-core==0.3.40)

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

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

Author: dependabot[bot]