major refactor(game-modes): centralize scoring and turn handling

* Move common ball recording, scoring, and turn-switching logic into `BaseMode`
* Add hooks for mode-specific ball handling and turn behavior
* Simplify 8-ball and 9-ball modes to use `LastBallMode`
* Update Snooker to use the new ball-processing hooks
* Remove duplicated scoring and turn-management code

controllers/game/modes/last_ball_mode.gd

@@ -0,0 +1,16 @@
+class_name LastBallMode extends BaseMode
+
+
+@export var final_ball_name: String = ""
+
+
+func on_ball_reaped(ball: Node3D) -> void:
+	if ball.name == final_ball_name:
+		ball_states[ball.name]["is_foul"] = true
+
+func on_ball_sunk(ball: Node3D) -> void:
+	if ball.name == final_ball_name:
+		ball_states[ball.name]["is_foul"] = true
+
+func process_win_condition() -> void:
+	pass