fix: replace generic exit 1 with specific exit codes in ct/ and install/ scripts

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)

misc/error_handler.func

@@ -195,6 +195,14 @@ if ! declare -f explain_exit_code &>/dev/null; then
     247) echo "Node.js: Fatal internal error" ;;
     248) echo "Node.js: Invalid C++ addon / N-API failure" ;;
     249) echo "npm/pnpm/yarn: Unknown fatal error" ;;
+
+    # --- Application Install/Update Errors (250-254) ---
+    250) echo "App: Download failed or version not determined" ;;
+    251) echo "App: File extraction failed (corrupt or incomplete archive)" ;;
+    252) echo "App: Required file or resource not found" ;;
+    253) echo "App: Data migration required — update aborted" ;;
+    254) echo "App: User declined prompt or input timed out" ;;
+
     255) echo "DPKG: Fatal internal error" ;;
     *) echo "Unknown error" ;;
     esac