refactor(checks): data-driven app requirements (collapse per-service case arms)

The 5 service arms in appInstallCheckRequirements (traefik/gluetun/authelia/
headscale/prometheus) were identical _appReqServiceInstalled calls. Collapse them
into one generic default: any requirement naming a real container is a service
prerequisite — so a new service requirement now needs NO code here, just list it
in the app's CFG_<APP>_REQUIRES. domain + mail stay as their own special types; a
requirement that isn't a known app is still treated as a typo and ignored (safety
net preserved). Flavor messages kept via a small optional reason map
(_appReqServiceMsg); unknown-to-the-map services get a clean generic message.

Stays central (it's the requirements engine, not per-app logic) but is now
extensible without edits. Verified with stubs: met→rc0, absent service→flavor or
generic msg, brand-new container service→generic (zero code), typo→ignored.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>
Signed-off-by: librelad <librelad@digitalangels.vip>

scripts/checks/requirements/check_app_install.sh

@@ -4,8 +4,12 @@
 #
 # Each app declares its prerequisites in its .config as
 #   CFG_<APP>_REQUIRES="<csv>"
-# where <csv> is a comma-separated list of requirement keys (see the
+# where <csv> is a comma-separated list of requirement keys: the special types
-# `case` arms below for the full set). Examples:
+#   domain  — at least one CFG_DOMAIN_N is set
+#   mail    — global mail is enabled
+# or the name of any other app/service that must be installed first. The service
+# case is data-driven — any real container name works with NO code change here,
+# just list it. Examples:
 #   CFG_AUTHELIA_REQUIRES="domain,traefik"
 #   CFG_BOOKSTACK_REQUIRES="domain,traefik"
 #
@@ -40,38 +44,23 @@ appInstallCheckRequirements()
                     missing+=("Set at least one CFG_DOMAIN_N (General → Network) before installing $app_name.")
                 fi
                 ;;
-            "traefik")
-                if ! _appReqServiceInstalled "traefik"; then
-                    missing+=("Install Traefik first — $app_name needs a reverse proxy to publish itself.")
-                fi
-                ;;
-            "gluetun")
-                if ! _appReqServiceInstalled "gluetun"; then
-                    missing+=("Install Gluetun first — $app_name expects a VPN gateway to route through.")
-                fi
-                ;;
-            "authelia")
-                if ! _appReqServiceInstalled "authelia"; then
-                    missing+=("Install Authelia first — $app_name's auth integration depends on it.")
-                fi
-                ;;
-            "headscale")
-                if ! _appReqServiceInstalled "headscale"; then
-                    missing+=("Install Headscale first.")
-                fi
-                ;;
-            "prometheus")
-                if ! _appReqServiceInstalled "prometheus"; then
-                    missing+=("Install Prometheus first — $app_name has nothing to query without it.")
-                fi
-                ;;
             "mail")
                 if [[ "$CFG_MAIL_ENABLED" != "true" ]]; then
                     missing+=("Configure global mail (CFG_MAIL_ENABLED=true under General → Mail) first.")
                 fi
                 ;;
             *)
-                isNotice "Unknown requirement '$req' declared by $app_name — ignoring."
+                # Any other requirement names a service/app that must be installed.
+                # Data-driven: if it's a real container it's a service prerequisite —
+                # adding a new one needs NO code here, just list it in the app's
+                # CFG_<APP>_REQUIRES. A name that's not a known app is a typo → ignore.
+                if [[ -d "${install_containers_dir}${req}" ]]; then
+                    if ! _appReqServiceInstalled "$req"; then
+                        missing+=("$(_appReqServiceMsg "$req" "$app_name")")
+                    fi
+                else
+                    isNotice "Unknown requirement '$req' declared by $app_name — ignoring."
+                fi
                 ;;
         esac
     done
@@ -88,6 +77,26 @@ appInstallCheckRequirements()
     return 0
 }
 
+# Human-friendly "install X first" line for a service prerequisite. Known services
+# get a reason; anything else falls back to a generic message — so a NEW service
+# requirement works with no code change (add a reason here only if you want flavor).
+_appReqServiceMsg()
+{
+    local svc="$1" app="$2" reason=""
+    case "$svc" in
+        traefik)    reason="a reverse proxy to publish itself" ;;
+        gluetun)    reason="a VPN gateway to route through" ;;
+        authelia)   reason="its auth integration" ;;
+        prometheus) reason="something to query" ;;
+    esac
+    local disp="$(tr '[:lower:]' '[:upper:]' <<< ${svc:0:1})${svc:1}"
+    if [[ -n "$reason" ]]; then
+        echo "Install $disp first — $app needs $reason."
+    else
+        echo "Install $disp first — required by $app."
+    fi
+}
+
 # True if any CFG_DOMAIN_<n> is set to a non-empty value.
 _appReqHasDomain()
 {