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)

ct/vikunja.sh

@@ -34,14 +34,14 @@ function update_script() {
     msg_warn "This requires MANUAL config changes in /etc/vikunja/config.yml."
     msg_warn "See: https://vikunja.io/changelog/whats-new-in-vikunja-1.0.0/#config-changes"
 
-    read -rp "Continue with update? (y to proceed): " -t 30 CONFIRM1 || exit 1
+    read -rp "Continue with update? (y to proceed): " -t 30 CONFIRM1 || exit 254
     [[ "$CONFIRM1" =~ ^[yY]$ ]] || exit 0
 
     echo
     msg_warn "Vikunja may not start after the update until you manually adjust the config."
     msg_warn "Details: https://vikunja.io/changelog/whats-new-in-vikunja-1.0.0/#config-changes"
 
-    read -rp "Acknowledge and continue? (y): " -t 30 CONFIRM2 || exit 1
+    read -rp "Acknowledge and continue? (y): " -t 30 CONFIRM2 || exit 254
     [[ "$CONFIRM2" =~ ^[yY]$ ]] || exit 0
   fi