docs: add provenance comments — what was replaced, why, what was removed

Each action.yml now documents:
- Original upstream repo (GitHub Actions)
- Why it was rewritten for self-hosted Gitea
- What was removed from the original
- Author and date

checkout/action.yml

@@ -1,3 +1,13 @@
+# Tinqs Checkout — replaces actions/checkout@v4
+# Original: https://github.com/actions/checkout (GitHub-hosted, Node.js action)
+# Why rewritten: actions/checkout requires Node.js runtime and GitHub API calls.
+#   On self-hosted Gitea (tinqs.com), it fails because it tries to hit api.github.com.
+#   This composite action uses plain git clone — works on any runner with git installed.
+# Removed from original: submodules, LFS, sparse-checkout, GitHub token auth, persist-credentials.
+#   We only need depth, ref, and optional Gitea token for private repos.
+# Author: Ozan / Claude Code — 2026-05-22
+# Part of: tinqs/ci (Tinqs CI toolchain)
+
 name: 'Tinqs Checkout'
 description: 'Clone a Gitea repository (replaces actions/checkout)'