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/agent-author/references/contract.md

@@ -6,7 +6,7 @@ source_keys:
 
 # The agent description and body contract
 
-House contract, set by ADR-0020. The counts and the boundary targets are enforced by
+House contract. The counts and the boundary targets are enforced by
 `agent-audit`'s `scripts/validate.sh`; the prose patterns by the Vale styles it bundles; the
 judgment calls by its reference files.
 
@@ -40,9 +40,8 @@ Banned from a description; move it to the body or to `README.md`:
 - Restating the same trigger twice in two registers — a verb list, then the same verbs re-quoted
   as user phrasings. This is a FAIL, not a suggestion.
 
-**Do not open with an action verb.** "Reviews…", "Analyzes…", "Generates…" was the old house rule
-and ADR-0020 deleted it: the opener is `Use when`, matching every skill in this corpus, so one
-router reads one shape.
+**Do not open with an action verb.** The opener is `Use when`, matching every skill in this corpus,
+so one router reads one shape.
 
 **"Use proactively" is Claude Code-only, and conditional even there.** The phrase steers the
 Claude Code runtime to offer an agent unprompted and does nothing anywhere else, so where it may