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-author/references/sources.md

@@ -34,7 +34,7 @@ source_keys:
 - **URL:** https://agentskills.io/skill-creation/best-practices.md
 - **Research doc:** plugins/kyberforge/docs/research/docs/agentskillsio/sources.md
 - **Description:** Best practices for skill creators — starting from real expertise, spending context wisely, calibrating control, instruction patterns (gotchas, templates, checklists, validation loops)
-- **Contributing files:** SKILL.md, references/create.md, references/improve.md, references/contract.md, references/retrofit.md
+- **Contributing files:** SKILL.md, references/create.md, references/improve.md, references/contract.md
 - **Status:** `extracted`
 
 ## agentskills-optimizing-descriptions
@@ -42,7 +42,7 @@ source_keys:
 - **URL:** https://agentskills.io/skill-creation/optimizing-descriptions.md
 - **Research doc:** plugins/kyberforge/docs/research/docs/agentskillsio/sources.md
 - **Description:** How to systematically test and improve skill descriptions for triggering accuracy — eval queries, trigger rate testing, train/validation splits, optimization loop
-- **Contributing files:** SKILL.md, references/improve.md, references/contract.md, references/retrofit.md
+- **Contributing files:** SKILL.md, references/improve.md, references/contract.md
 - **Status:** `extracted`
 
 ## agentskills-evaluating-skills