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-submodules/references/README.md

@@ -1,31 +0,0 @@
----
-source_keys:
-  - git-scm-submodule-docs
----
-
-# References
-
-One file per task branch in SKILL.md's dispatch table. Load only the one that matches the request.
-
-## setup-and-update.md
-
-Cloning a superproject that has submodules, adding a dependency as a submodule, initializing
-without cloning, updating or re-pinning, and running one command across every submodule. Carries
-the `add` and `update` flag tables, the keep-pinned and move-the-pin-forward workflows, and the
-`foreach` shell-variable table (`$name`, `$sm_path`, `$displaypath`, `$sha1`, `$toplevel`).
-
-## urls-and-config.md
-
-Where a submodule points and how it is configured: the `.gitmodules` vs `.git/config` split, both
-key tables, `sync` / `set-url` / `set-branch`, local mirror overrides, relative URL resolution, the
-security gate on custom `update` commands, and `absorbgitdirs`.
-
-## removal.md
-
-Removing a submodule, and why `deinit` alone does not remove one. Carries the full four-step
-removal sequence including the manual `.git/modules/<name>/` cleanup.
-
-## sources.md
-
-Research sources that informed this skill — provenance chain for git-scm-submodule-docs reference
-material.