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-branches/references/branch-operations.md

@@ -45,10 +45,10 @@ past it: it shelves the working tree and index so the branch pointer can move.
   reports `No local changes to save` and stashes nothing. Bare `git stash` is `push` with no message.
 - **restore** — `git stash pop` applies the newest entry and deletes it. Bare, not `rtk`: on a
   conflict rtk prints only `FAILED: git stash pop` and swallows the conflict report the paragraph
-  below tells you to read (ADR-0023). `rtk git stash apply stash@{n}`
+  below tells you to read. `rtk git stash apply stash@{n}`
   applies without deleting, for replaying one shelf onto more than one branch.
 - **list** — `git stash list` — bare, not `rtk`: rtk prints `No stashes` where git prints nothing,
-  so an empty-output test misfires (ADR-0023). `rtk git stash show -p stash@{n}` prints that entry's diff.
+  so an empty-output test misfires. `rtk git stash show -p stash@{n}` prints that entry's diff.
 - **drop** — `rtk git stash drop stash@{n}` deletes one entry. `rtk git stash clear` deletes all of them
   and nothing recovers them — confirm before running it.
 - **branch from a stash** — `rtk git stash branch <branch> stash@{n}` creates a branch at the commit the