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/skills/git-worktrees/references/README.md

@@ -1,13 +0,0 @@
----
-source_keys:
-  - git-scm-worktree-docs
----
-
-# References
-
-This directory contains provenance metadata and research sources for the `git-worktrees` skill.
-
-## Files
-
-- `sources.md` — Extracted research sources and their contributing documents
-- `worktrees.md` — Shared vs. per-worktree state, the `add` command forms, the full `add` flag table, orphan branches, sparse-checkout setup, removable-media locking, remote-branch disambiguation, where to run `repair` from, the config key reference, and the emergency-fix and PR-review workflow patterns