docs: align docs with Amaru relay bootstrap

[paolino]

Summary

• Reframe README and MkDocs landing pages around the long-lived amaru-relay-bootstrap Antithesis relay model
• Add an Antithesis deployment page documenting topology, env vars, startup markers, retry behavior, and amaru-runtime/ files
• Replace the stale one-shot tutorial and move the old bundle-rationale page into docs history

Closes #40

Verification

• nix develop github:paolino/dev-assets?dir=mkdocs --quiet -c mkdocs build --strict --site-dir /tmp/amaru-bootstrap-docs-build