feat: add controller-side healthcheck configs to all 52 apps

Each app template now declares a healthcheck: section in .felhom.yml
with appropriate probe type (http, api, or tcp) and endpoint based on
the app's known health endpoints. The controller uses these to verify
services are actually responding, not just that containers are running.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

templates/nextcloud/.felhom.yml

@@ -89,3 +89,13 @@ app_info:
     - 'Külső HDD szükséges a fájlok tárolásához'
     - 'Legalább 1 GB szabad RAM (Nextcloud + MariaDB + Redis)'
     - 'x86 processzor ajánlott a legjobb teljesítményhez'
+
+# --- Controller-side health probe ---
+healthcheck:
+  checks:
+    - type: api
+      port: 80
+      path: "/status.php"
+      expect:
+        status: 200
+        body_contains: "installed"