fix: replace generic exit 1 with specific exit codes in ct/ and install/ scripts (#12475)

Part of #12467 — scripts only (no framework changes).

New exit codes 250-254 registered in api.func and error_handler.func:
- 250: App download failed or version not determined
- 251: App file extraction failed (corrupt/incomplete archive)
- 252: App required file or resource not found
- 253: App data migration required — update aborted
- 254: App user declined prompt or input timed out

Existing codes reused where applicable:
- 10: privileged/Docker required (unifi-os-server)
- 64: invalid user input (postgresql, tomcat)
- 71: system error (pulse useradd)
- 150: service failed to start (docker, npmplus)
- 153: build failed (booklore)
- 233: app not installed (evcc, endurain, grafana, loki, itsm-ng)
- 236: hardware not detected (unifi-os-server /dev/net/tun)
- 238: OS not supported (frigate)

install/splunk-enterprise-install.sh

@@ -34,7 +34,7 @@ while true; do
         [Nn]|[Nn][Oo]|"")
             msg_error "Terms not accepted. Installation cannot proceed."
             msg_error "Please review the terms and run the script again if you wish to proceed."
-            exit 1
+            exit 254
             ;;
         *)
             msg_error "Invalid response. Please enter 'y' for yes or 'n' for no."
@@ -47,7 +47,7 @@ DOWNLOAD_URL=$(curl -s "https://www.splunk.com/en_us/download/splunk-enterprise.
 RELEASE=$(echo "$DOWNLOAD_URL" | sed 's|.*/releases/\([^/]*\)/.*|\1|')
 $STD curl -fsSL -o "splunk-enterprise.tgz" "$DOWNLOAD_URL" || {
     msg_error "Failed to download Splunk Enterprise from the provided link."
-    exit 1
+    exit 250
 }
 $STD tar -xzf "splunk-enterprise.tgz" -C /opt
 rm -f "splunk-enterprise.tgz"