docs: make verified quickstart the first path

[abrichr]

What changed

• Make the verified two-command local tutorial the primary installation path.
• Explain the five record, compile, certify, run, and verify stages.
• Add a short fail-safe halt exercise.
• Keep native and remote installs lightweight and browser-free.
• Redirect the legacy quickstart route to the current guide.

Why

The former page required users to assemble the tutorial lifecycle by hand. The launcher now delegates to Flow's verified tutorial, so the documentation can give one canonical path with a local receipt.

Checks

• Canonical Docs validation passed
• Eight focused tests passed
• Strict MkDocs build passed
• Diff check passed