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).

.gitmodules

@@ -0,0 +1,4 @@
+[submodule "docs.coopcloud.tech"]
+	path = docs.coopcloud.tech
+	url = https://git.coopcloud.tech/toolshed/docs.coopcloud.tech.git
+	branch = main