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/.apm/skills/skill-author/tests/new-skill.bats

@@ -34,11 +34,6 @@ teardown() {
     assert [ -f "$DEST/my-tool/SKILL.md" ]
 }
 
-@test "scaffold contains README.md" {
-    bash "$SCRIPT" my-tool "$DEST"
-    assert [ -f "$DEST/my-tool/README.md" ]
-}
-
 @test "scaffold contains scripts/, references/, assets/, tests/ directories" {
     bash "$SCRIPT" my-tool "$DEST"
     assert [ -d "$DEST/my-tool/scripts" ]
@@ -53,12 +48,6 @@ teardown() {
     assert_success
 }
 
-@test "substitutes skill name in README.md" {
-    bash "$SCRIPT" my-tool "$DEST"
-    run grep "my-tool" "$DEST/my-tool/README.md"
-    assert_success
-}
-
 @test "substitutes skill name in tests/README.md" {
     bash "$SCRIPT" my-tool "$DEST"
     run grep "my-tool" "$DEST/my-tool/tests/README.md"