Release v2.2.0

Release v2.2.0: bookkeeping only, no standard, template or check changes.

VERSION to v2.2.0, reference_version propagated by just sync to the root .reference.yaml and the four template copies, and CHANGELOG's [Unreleased] renamed to the 2.2.0 heading.

Consumers can then declare reference_version: v2.2.0, the first release whose pipeline standard accepts a @6 catalog major pin.

Standards affected: none changed here. pipeline's pin assertion landed in !107 (merged) and ships in this tag; the forms it newly rejects (@6.2.2, @v6, @v6.2) never resolved on the platform, so no consumer with a starting pipeline breaks. No exemption registration implied.

just ship green locally: 21 standards pass, versions consistent at reference v2.2.0 / catalog 6, and validate-release-notes confirms the tag body extracts.