chore: add uv.lock for uv package manager

Migrate from pipenv to uv for faster, more reliable dependency management.
uv.lock replaces Pipfile.lock for dependency locking.

To use uv:
- Install: curl -LsSf https://astral.sh/uv/install.sh | sh
- Sync deps: uv sync --all-extras
- Run tests: uv run pytest

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: jon-myers