Keep World Library docs scoped to shipped examples

[everettVT]

Summary

• make the README explicit that Biome is the only shipped example
• remove the Holocron-specific narrative from the public World Library document
• preserve the cross-domain insight as an extraction rule: a second independent implementation must reproduce a seam before it becomes a generic Archetype abstraction

Why

Holocron is maintained separately and is not present in this public repository. The document should not claim an executable proof that readers cannot inspect here.

Verification

• no Holocron references remain in README, docs, source, tests, or examples
• uv run ruff check .
• uv run pytest -q — 2 passed
• git diff --check