chore(review): drop the one-release review-digest team fallbacks #13556

Refs #5906

Outcome

/review:explain-change reads its team settings only from docs/conventions/review-digest.yaml. The one-release fallbacks to the ```json config block in docs/conventions/review-digest.md and to .claude/review-digest.json are gone. The YAML reader shipped with "read only when the YAML file is absent from the base commit, for one release" (plugins/review/CHANGELOG.md:694), and the plugin is at 7.4.0 now. #5906's verify run on 2026-11-05 parked it with this item unmet (its outcome=parked comment). The user-global ~/.claude/review-digest.json and the personal .claude/review-digest.local.json layers stay.

Change

• plugins/review/skills/explain-change/scripts/digest-policy.mjs:
  • readTeamDigest (:205-241, called at :262) takes the team layer from docs/conventions/review-digest.yaml only.
  • Delete configBlock (:125-148); its only caller is the fallback at :219.
  • Drop the docs/conventions/review-digest.md and .claude/review-digest.json entries from the team-file list (:251) and from the readTeamDigest call (:262).
  • Remove docs/conventions/review-digest.md (:40) and .claude/review-digest.json (:41) from CONFIG_PATHS, since neither is read any more.
  • Keep .claude/review-digest.local.json (:42) and the user-global review-digest.json filename (:250).
• docs/conventions/review-digest.md: remove the ```json config block and its note (:85-98), and rewrite list item 2 (:54-57) to say the team layer is docs/conventions/review-digest.yaml only.
• docs/contracts/config-cascade/README.md:595 and :673: describe the review-digest team layer as the YAML file only, and drop the "old pair" and ADR 0044 sentences in those rows.
• plugins/review/tests/explain-change.test.mjs:
  • Remove the configBlock import (:31), its describe (:179-191), and the block comparison at :198-199.
  • Rewrite the cases at :226-238, :298-309, :343-349 and :383-389 to use the YAML file, with review-digest.yaml as the risk-path witness path at :389.
  • Add assertions that a tracked docs/conventions/review-digest.md json-config block and a tracked .claude/review-digest.json are not read.
• Add a review changelog fragment.

Done when

• git grep -n 'claude/review-digest\.json' -- plugins/review/skills/explain-change/scripts/digest-policy.mjs prints nothing (3 lines on origin/main today: :41, :251, :262).
• git grep -n 'json config' -- docs/conventions/review-digest.md plugins/review/skills/explain-change/scripts/digest-policy.mjs prints nothing (4 lines today: review-digest.md:55 and :89, digest-policy.mjs:125 and :140).
• git grep -n 'review-digest.json' -- docs/contracts/config-cascade/README.md prints nothing (:595 and :673 today).
• node --test plugins/review/tests/explain-change.test.mjs passes in the PR's CI.
• scripts/check-changelog-fragments.sh --check-required origin/main exits 0.