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/kyberforge/.apm/skills/skill-author/references/create.md

@@ -84,7 +84,7 @@ already covers the new skill. Use Read/Edit directly on `apm.yml`; this is not p
 ## Step 3 — Fill in SKILL.md
 
 Open the new skill's `SKILL.md` (the path Step 1 printed) and replace every `FILL IN:`
-placeholder. The scaffold template carries the ADR-0020 body skeleton and the two frontmatter
+placeholder. The scaffold template carries the body skeleton and the two frontmatter
 fields that cannot be left as placeholders — `name`, substituted by the script, and
 `metadata.version`, seeded live at `"0.1.0"` — so fill the template in rather than restructuring
 it.