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-history/SKILL.md

@@ -8,7 +8,7 @@ description: >
   `git-commits`. Not a Gitea server's history -> `gitea-branches`.
 
 metadata:
-  version: "1.0.1"
+  version: "1.0.2"
   category: git
   source_keys:
     - git-scm-bisect-docs
@@ -38,7 +38,7 @@ allowed-tools: Bash
 Default to `rtk git log --oneline`, then narrow by whatever is known:
 
 - **Content**: `rtk git log -S"string"`, or `-G"regex"` to match any diff line. `--pickaxe-regex` makes the `-S` argument a POSIX ERE; `--pickaxe-all` shows every file in a matching changeset.
-- **A line or function**: `git log -L <start>,<end>:<file>` or `git log -L :<function>:<file>` — bare, not `rtk`: rtk truncates each diff line at ~72 characters (ADR-0023). Confirm the range resolves before reporting on it — an off-by-one silently omits the target.
+- **A line or function**: `git log -L <start>,<end>:<file>` or `git log -L :<function>:<file>` — bare, not `rtk`: rtk truncates each diff line at ~72 characters. Confirm the range resolves before reporting on it — an off-by-one silently omits the target.
 - **A file across renames**: `rtk git log --follow -- <file>`. Without `--follow` the history stops at the rename boundary.
 - **Mainline only**: `--first-parent` follows the integration branch and skips commits merged in from side branches.
 - **Structured output**: `rtk git log --format="%h | %s | %an (%ar)"`.