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/test.md

@@ -0,0 +1,14 @@
+# Custom HTML Tests
+
+## Target
+
+- **URL:** https://custom-html.<DOMAIN_SUFFIX>
+
+## Automated Checks
+
+- `health_check.py` — Confirms the instance is reachable and returns HTTP 200.
+
+## Manual Verification
+
+1. Open https://custom-html.<DOMAIN_SUFFIX> in a browser.
+2. Confirm the nginx default page (or custom HTML content) loads without errors.