fix(match): guard kickoff countdown against a post-match resume

The coroutine stalls mid-countdown while the tree is paused for the
results screen, but _end_match unpauses before the deferred scene
change actually tears things down — letting it resume for a frame and
re-emit kickoff_countdown / unfreeze bodies in the dying scene.

Game/scripts/match_mode.gd

@@ -29,6 +29,7 @@ const KICKOFF_COUNTDOWN_SECONDS := 3
 
 var match_timer: Timer
 var _in_overtime := false
+var _match_over := false
 
 
 func _get_arena_scene_path() -> String:
@@ -67,6 +68,8 @@ func _process(_delta):
 
 
 func _on_goal_scored(conceding_team: int) -> void:
+	if _match_over:
+		return
 	var scoring_team := 1 - conceding_team
 	_record_goal(scoring_team)
 	score_changed.emit(score.duplicate())
@@ -82,6 +85,8 @@ func _on_goal_scored(conceding_team: int) -> void:
 # changes to ship.gd/ball.gd/ship_controller.gd, keeping training_mode.gd
 # (which never calls into this file) completely untouched.
 func _run_kickoff_countdown() -> void:
+	if _match_over:
+		return
 	reset_ball()
 	reset_ships()
 	_set_frozen(true)
@@ -90,8 +95,12 @@ func _run_kickoff_countdown() -> void:
 		# process_always=false: if full-time fires mid-countdown (see
 		# _on_match_timer_timeout's get_tree().paused = true), this stalls
 		# harmlessly in lockstep with the pause instead of ticking a
-		# countdown label over the results screen.
+		# countdown label over the results screen. _end_match unpauses the
+		# tree before the scene teardown actually lands, so the _match_over
+		# check below is what stops this from resuming into a dying scene.
 		await get_tree().create_timer(1.0, false).timeout
+		if _match_over:
+			return
 	kickoff_countdown.emit(0)
 	_set_frozen(false)
 
@@ -121,6 +130,7 @@ func _start_overtime() -> void:
 
 
 func _end_match(winning_team: int) -> void:
+	_match_over = true
 	print("Match over! Final score: %d - %d" % [score[0], score[1]])
 	match_ended.emit(winning_team, score.duplicate())
 	# Freeze gameplay while the HUD (process_mode ALWAYS) shows the result.