Make alpha quickstart install self-contained

[YuzeJ21]

Summary

• add the current v0.2.1 release-wheel install path directly to the public-alpha participant quickstart
• include benchmark and local workbench launch commands before the ten-minute path
• add repository-contract coverage so the quickstart stays public-release based and Stage-safe

Verification

• uv run pytest -q tests/test_repository_contracts.py::test_public_alpha_participant_kit_is_safe_complete_and_actionable
• uv run pytest -q tests/test_repository_contracts.py
• uv run ruff check tests/test_repository_contracts.py
• git diff --check

Boundaries

• no release publication
• no outreach or external validation claim
• v0.2.2 remains internal
• setup success remains engineering/setup evidence only and does not advance Stage 1