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_ui.py

@@ -0,0 +1,49 @@
+"""libredesk — UI probe: the served root HTML is the real LibreDesk app, not a fallback page.
+
+/health passing only proves the process is up. This asserts the front-end SPA is actually bound and
+serving its own shell — a wedged backend or a misrouted proxy would 200 with generic/empty content.
+"""
+
+from __future__ import annotations
+
+import os
+import ssl
+import sys
+import urllib.request
+
+sys.path.insert(0, os.path.join(os.path.dirname(__file__), "..", "..", "..", "runner"))
+from harness import http as harness_http  # noqa: E402
+
+_CTX = ssl.create_default_context()
+_CTX.check_hostname = False
+_CTX.verify_mode = ssl.CERT_NONE
+
+
+def _get_body(url: str) -> tuple[int, str]:
+    req = urllib.request.Request(url, method="GET")
+    with urllib.request.urlopen(req, timeout=15, context=_CTX) as r:
+        return r.status, r.read().decode(errors="replace")
+
+
+def test_libredesk_serves_app_shell(live_app):
+    """GET /; assert LibreDesk-specific brand or SPA-asset markers in the served HTML."""
+    url = f"https://{live_app}/"
+
+    def _ready():
+        try:
+            status, body = _get_body(url)
+        except Exception:  # noqa: BLE001
+            return None
+        return body if status in (200, 301, 302) else None
+
+    body = harness_http.assert_converges(_ready, f"GET {url}", max_wait=120, interval=5)
+    lower = body.lower()
+
+    # Brand markers: the app title / meta / bundle references carry "libredesk".
+    brand = [m for m in ("libredesk", "libre desk") if m in lower]
+    # SPA asset markers: the built front-end serves hashed JS/CSS bundles + a favicon.
+    assets = [m for m in ("/assets/", "favicon", ".js", ".css", "<div id=\"app\"", "id=app") if m in body]
+
+    assert brand or assets, (
+        f"GET {url} HTML has no LibreDesk brand or SPA-asset markers. Excerpt: {body[:300]!r}"
+    )