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/emqx-install.sh

@@ -21,7 +21,7 @@ msg_info "Fetching latest EMQX Enterprise version"
 LATEST_VERSION=$(curl -fsSL https://www.emqx.com/en/downloads/enterprise | grep -oP '/en/downloads/enterprise/v\K[0-9]+\.[0-9]+\.[0-9]+' | sort -V | tail -n1)
 if [[ -z "$LATEST_VERSION" ]]; then
   msg_error "Failed to determine latest EMQX version"
-  exit 1
+  exit 250
 fi
 msg_ok "Latest version: v$LATEST_VERSION"