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/skills/skill-audit/references/validation-scripts.md

@@ -21,7 +21,7 @@ have checked, and the Step 4 coverage line then names a dimension nothing actual
 ## Manual structural fallback
 
 `validate.sh` needs `python3` **and** PyYAML, and refuses to start without either — the description
-value has to be measured after YAML folding is resolved, so skipping the ADR-0020 gates would be a
+value has to be measured after YAML folding is resolved, so skipping these gates would be a
 vacuous pass rather than a partial one. The two are checked separately, so the message already names
 the right one — report it verbatim rather than diagnosing further:
 
@@ -40,14 +40,14 @@ by hand and file the results under `### Structure` exactly as the script's outpu
   session, so a skill without one can never be routed to.
 - **Description length**, measured on the folded YAML value with newlines collapsed to single
   spaces — not on the raw block scalar, which counts indentation. 250 characters SUGGESTION, 400
-  FAIL (ADR-0020), 1,024 FAIL (agentskills.io spec).
+  FAIL (house), 1,024 FAIL (agentskills.io spec).
 - **Body length**, counting everything after the frontmatter's closing `---`. 600 words
-  SUGGESTION, 900 FAIL (ADR-0020).
+  SUGGESTION, 900 FAIL (house).
 - **Whole-file ceilings**, counting the file including frontmatter: 500 lines FAIL, 2,770 words
   FAIL (agentskills.io spec). These are a different measurement from the two above — report them
   as separate findings, never merged.
 - **A boundary clause is present** — either the prose form (`do not` / `instead` / `rather than` /
-  `not for`) or ADR-0020's compressed `Not <thing> -> <name>` arrow. **SUGGESTION**, not FAIL:
+  `not for`) or the compressed `Not <thing> -> <name>` arrow. **SUGGESTION**, not FAIL:
   the absence is deterministic, but whether this skill warrants one is the auditor's call.
 - **Boundary targets resolve** — **FAIL** on a name that resolves to nothing. See the section
   below; resolving these by hand is the one item on this list with a procedure of its own.