docs: trim skill READMEs and ADR/changelog narration

Two related simplification-audit findings, bundled because they edit
some of the same skill-audit files and splitting would fragment
single-file diffs.

Finding 10: delete 48 per-skill/reference README.md files (they
restated SKILL.md in narrative form and no agent ever loads them) plus
2 scaffold templates. Drop the README criterion from skill-audit's
file-structure.md and finding-criteria.md, and the README-generation
step from skill-author's new-skill.sh; update new-skill.bats to match.
Plugin-root READMEs are kept intentionally, out of scope.

Finding 12: strip historical ADR-0020/ADR-0023 citations and
changelog-style narration from model-facing skill content across
kyberforge and git plugin skills. Delete skill-author's one-time
retrofit.md migration guide and its references. Some ADR-0023 tags
were not narration but check-rtk-prefix's required opt-out marker for
intentionally-bare git commands -- those were restored, not stripped.

Mirror re-synced and full pre-commit/pre-push suite verified green.

Refs: SIMPLIFICATION-AUDIT.md findings 10, 12

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01YR2CjVumUbEGWcMikcoXBD

plugins/git/.apm/skills/git-remotes/references/push.md

@@ -50,7 +50,7 @@ Two mitigations:
 # poisoned by an unrelated fetch.
 # The inner `git config` is bare: its stdout becomes a remote URL, so any
 # output rewriting would poison the remote silently.
-rtk git remote add origin-push $(git config remote.origin.url)   # inner bare per ADR-0023
+rtk git remote add origin-push $(git config remote.origin.url)   # inner bare (ADR-0023)
 rtk git push --force-with-lease origin-push
 
 # Option 2 — explicit SHA via a local tag, unaffected by tracking-branch state