🔧 chore(deps): regenerate stale uv.lock (langchain-core constraint)

uv.lock was out of sync with pyproject.toml's langchain-test group
(langchain-core specifier <1.5.0 in the lock vs <1.6.0 in
pyproject.toml, left behind by #296's constraint bump). This was
failing every PR's CI with `uv sync --locked` erroring "lockfile
needs to be updated" — including dependency-upgrade PRs that don't
touch pyproject.toml/uv.lock at all (e.g. #297, actions/setup-uv).

Verified: unit (1131 passed) and integration (38 passed) suites both
green with the regenerated lock.

Author: Chisanan232