Add uv.lock for dependency locking

Generated uv.lock file to pin exact dependency versions. This also
eliminates the CI warning about missing cache dependency files, since
astral-sh/setup-uv@v5 now has uv.lock to use as a cache key.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

Author: ryan-williams