recipe-maintainer: public snapshot (secrets + deployment plans removed, single commit)

Sanitized single-commit public mirror of recipe-maintainer.
- Removed test-ssh/.testenv (live creds); added test-ssh/.testenv.example placeholders.
- Removed plans/ and planned-updates/ (deployment-planning docs) so no client/
  deployment domains appear in the public repo.
- All other secret stores were already gitignored.
- docs.coopcloud.tech retained as a submodule (public upstream).

recipe-info/custom-html/upstream.md

@@ -0,0 +1,14 @@
+# Custom HTML Upstream
+
+## Main Project
+
+- **Recipe:** https://git.coopcloud.tech/coop-cloud/custom-html
+- **nginx:** https://nginx.org
+
+## Images
+
+| Service | Image | Release Notes |
+|---------|-------|---------------|
+| app | `nginx` | https://nginx.org/en/CHANGES |
+| git | `alpine/git` | https://github.com/alpine-docker/git/releases |
+| ssh | `linuxserver/openssh-server` | https://github.com/linuxserver/docker-openssh-server/releases |