docs: record maintenance closeout surface

[tryskian]

Summary

• Record the Polinko-style licence presentation and package metadata decision.
• Record Ruff as the import-sorting authority after retiring the separate isort surface.
• Update the runbook and session handoff with the current maintenance and closeout process.

Validation

• make lint-docs
• git diff --check
• make end-preflight
• make end on the feature branch, with only the expected final git closeout failure because the branch is not clean synced main yet.