tests: add libredesk (LibreDesk helpdesk) recipe test suite

New recipe recipe-maintainers/Libre-Desk (abra TYPE=libredesk): app libredesk
v2.4.0 on :9000 + postgres:17 + redis:7. Adds:
- recipe_meta.py: /health probe, BACKUP_CAPABLE (backupbot db labels), upgrade
  EXPECTED_NA (only one published version so far), WARM_CANONICAL.
- install_steps.sh: insert format-compliant enc_key (32-hex) + admin_pwd
  (upper+lower+num+special) before deploy — abra's generic generator doesn't
  satisfy LibreDesk's strict secret formats.
- custom/: /health 200 probe + served-shell brand/asset probe (real app, not a
  fallback 200).

tests/libredesk/custom/test_health.py

@@ -0,0 +1,20 @@
+"""libredesk — health check: the app's /health endpoint responds 200 through Traefik.
+
+This is the same endpoint the compose healthcheck hits internally (:9000/health); exercising it via
+the public domain confirms the app is bound and the proxy route is wired.
+"""
+
+from __future__ import annotations
+
+import os
+import sys
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "runner"))
+from harness import http as harness_http  # noqa: E402
+
+
+def test_libredesk_health(live_app):
+    """GET /health → 200."""
+    url = f"https://{live_app}/health"
+    status, _ = harness_http.retry_http_get(url, expect_status=(200,), max_wait=120, interval=5)
+    assert status == 200, f"GET {url} HTTP {status} (expected 200)"