Issue

CONTRIBUTING.md has stale local development setup guidance.

It links to a development setup guide that does not exist. It also does not
clearly explain that native Windows shells are not supported for the full dev
setup.

This can confuse new contributors. For example:

• PowerShell can fail because sh is missing.
• Git Bash can fail because Python packages such as uvloop do not support
  Windows.
• Missing tools such as jq or uv produce setup failures.

Proposed fix

Update the development setup section in CONTRIBUTING.md.

Add a small just doctor command that checks the local environment before
starting the stack.

The doctor command should check:

• Supported OS or shell
• git
• jq
• uv
• pnpm
• just
• Docker
• Docker Compose
• Docker daemon access

Expected result

New contributors can run:

just doctor
just cluster up -d --seed

If something is missing, just doctor tells them what to fix before the full
setup starts.