Add method to clear teams in GameManager

Introduced a `clearTeams` method in `GameManager` to reset the teams list. Updated `Main.java` to call this method, ensuring teams are cleared before processing.

src/main/java/com/alttd/ctf/Main.java

@@ -62,6 +62,7 @@ public class Main extends JavaPlugin {
             return;
         }
 
+        gameManager.clearTeams();
         teams.stream()
                 .collect(Collectors.groupingBy(Team::getId, Collectors.counting()))
                 .forEach((id, count) -> {

src/main/java/com/alttd/ctf/game/GameManager.java

@@ -80,4 +80,8 @@ public class GameManager {
         }
         return gamePhaseExecutor;
     }
+
+    public void clearTeams() {
+        teams.clear();
+    }
 }