feat(python): make Vyral one command from source

[jeremydixon22]

Summary

• make ./scripts/vyral the zero-install source-checkout experience
• expose vyral as the preferred installed command while retaining vyral-runtime as a compatibility alias
• make bare vyral run the safe, marker-bounded local proof
• move the shortest path near the top of the README and move manual setup into the Python runtime guide
• qualify both console entry points and the direct source launcher

Verification

• scripts/verify-python-runtime.sh
• scripts/verify-public-export.sh
• python3 scripts/verify-markdown-links.py --all .

Checklist

• The one-command path uses no package installation or third-party service.
• Explicit server and custom-root paths remain available.
• The legacy executable remains compatible.
• Public export was regenerated from a clean commit.