Migrate to uv

[asmithml]

This PR migrates the project from Pixi to UV as the Python package manager.

Changes Made

Dependency Management:

• Replaced Pixi with UV for all package management operations
• Updated pyproject.toml to use UV dependency groups (PEP 735)
• Production dependencies via uv sync, development via uv sync --group dev

CI/CD (.github/workflows/ci.yml):

• Replaced Pixi setup with Python 3.12 + UV installation using astral-sh/setup-uv@v5
• Updated all commands to use uv run instead of pixi run
• Reordered steps for fail-fast behavior (format → lint → type check → tests)

Deployment (deploy.sh):

• Updated EC2 deployment script to install UV instead of Pixi
• Changed systemd service to use uv run python run.py
• Updated PATH references from ~/.pixi/bin to ~/.local/bin
• Simplified service configuration (removed CONDA_OVERRIDE_GLIBC workaround)

Documentation (README.md):

• Updated installation instructions to use UV
• Replaced all pixi run commands with uv run equivalents
• Updated development workflow commands
• Direct Docker command for DynamoDB Local instead of Pixi task

Technical Notes

• GPU support maintained: PyTorch with CUDA 12 dependencies install automatically on Linux x86_64 via platform markers in uv.lock
• Pre-commit hooks unchanged (manages own environments)
• Python version requirement: 3.12 only
• Lock file (uv.lock) committed for reproducible builds

Testing

• CI workflow validates linting, formatting, type checking, and tests
• Deployment script tested for dependency installation flow