chore: delete the reference-check story everywhere it was told

Executes the 2026-08-07 decision. The component existed at no catalog tag, yet six commented pins referenced it at two versions, two SKILL.md files asserted its behaviour as fact, the site's home diagram said "conform via reference-check", and Renovate regenerated an impossible major-bump MR against the phantom pin every run.

Removed from README, AGENTS.md, .gitlab-ci.yml, deviations.yaml, both version scripts (exclusions deleted as dead code), two SKILL.mds, four template .reference.yaml headers, four template CI blocks, and eight site pages including both SVG diagrams. What remains is what was always real: clone the reference at a pinned tag, just check REPO=$CI_PROJECT_DIR.

Stacked on !67 (merged); merge that first. Closes the story tracked in !13 (closed).