Fix security vulnerabilities: update vulnerable dependencies

[bjoernbethge]

Summary

• Add explicit minimum version constraints for 6 vulnerable transitive dependencies in [project.dependencies]: sqlparse>=0.5.3, diskcache>=5.6.3, pillow>=11.0.0, cryptography>=44.0.1, protobuf>=5.26.1, python-multipart>=0.0.18
• Add langchain-core>=0.3.15 and langsmith>=0.2.0 to [project.optional-dependencies].llm

Severity

• pillow, cryptography, protobuf, python-multipart — high
• sqlparse, langsmith, diskcache — medium
• langchain-core — low