Migrate Gradle wrapper to 8.14.5, clean IntelliJ and build artifacts, and update configuration handling

.gitignore

@@ -29,5 +29,15 @@ replay_pid*
 
 # End of https://www.toptal.com/developers/gitignore/api/java
 
+### Gradle ###
+.gradle/
+build/
+!gradle/wrapper/gradle-wrapper.jar
 
-run
+### IntelliJ ###
+.idea/
+*.iml
+out/
+
+### run-paper Testserver ###
+run/