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/.apm/skills/git-commits/references/rewrite-history.md

@@ -21,7 +21,7 @@ Prefer this whenever a commit is written to be folded, because git does the mark
 
 1. `rtk git commit --fixup=<commit>` keeps the target's message; `rtk git commit --squash=<commit>` lets you edit the combined message later. Both prefix the message with `fixup!`/`squash!` and name the target commit.
 2. Get explicit approval — the rebase still rewrites history.
-3. Run `git rebase -i --autosquash HEAD~N` — bare, not `rtk`: `-i` opens an interactive sequence editor (ADR-0023). Git pre-fills the todo list with the tagged commits already reordered against their targets; save it unchanged to apply.
+3. Run `git rebase -i --autosquash HEAD~N` — bare, not `rtk`: `-i` opens an interactive sequence editor. Git pre-fills the todo list with the tagged commits already reordered against their targets; save it unchanged to apply.
 
 **`-i` is not optional here.** On Git 2.39.5, `git rebase --autosquash HEAD~N` without `-i` prints `Successfully rebased and updated refs/heads/<branch>.` and exits 0 while leaving the `fixup!` commit in place at its original SHA — `--autosquash` is honoured only by the interactive machinery, and the false success is the trap: the fold is reported as done, and the surviving `fixup!` subject then fails the Conventional Commits `commit-msg` hook. Later Git versions taught the non-interactive rebase to honour the flag, but `-i --autosquash` is correct on every version, so always write that.