Switch to SIGTERM for graceful shutdown in startup.sh

Replaced the `curl` HTTP shutdown call with a `kill -TERM` signal to ensure the JVM shutdown hook executes cleanly. Added a `wait` command to block until the process finishes, enabling a more reliable and proper termination process.

startup.sh

@@ -6,9 +6,10 @@ _term() {
     echo "Bot isn't running, exiting."
     exit 0
   else
-    /usr/bin/curl --no-progress-meter http://localhost:"$API_PORT"/actions/shutdown
-    echo "Waiting 2 seconds for bot shutdown"
-    sleep 2
+    # SIGTERM triggers the JVM shutdown hook (App.shutdown); wait until it has finished.
+    kill -TERM "$pid" 2>/dev/null
+    wait "$pid"
+    exit $?
   fi
 }