chore: update .gitignore and build.gradle.kts for local server testing

- Added entries to .gitignore for local Paper test server and API documentation.
- Included the run-paper plugin in build.gradle.kts for local server execution.
- Configured runServer task with Minecraft version 1.21.4 for testing.

src/main/java/com/loki/lochat/commands/CustomCommand.java

@@ -35,4 +35,4 @@ public final class CustomCommand extends Command {
         // Базовое автодополнение - можно расширить при необходимости
         return new ArrayList<>();
     }
-}
+}