Simplify environment management options to uv, pip/venv, or conda

[josephwilson8-nhs]

Description:
Reduce environment management complexity to three clear options: uv, pip/venv, or conda.

Proposed Options:

1. uv (default, recommended) - Uses pyproject.toml
2. pip + venv - Uses pyproject.toml
3. conda - Uses environment.yml

Tasks:

• Simplify environment prompts in cookiecutter.json
• Generate pyproject.toml for uv and pip/venv options
• Generate environment.yml for conda option
• Update documentation with setup instructions for each
• Remove other environment management options
• Add Makefile targets for each option (setup, install, test, etc.)

Acceptance Criteria:

• Clear, simple choice between three options
• Each option is well-documented
• Generated files match selected option
• Setup instructions work for each option

Priority: High
Type: Refactor