feat(*): Add self-play RL training pipeline with PPO trainer, in-game GDScript policy inference, and bot opponent support in Match mode

Game/scripts/match_mode.gd

@@ -1,15 +1,22 @@
 extends GameMode
 
 # Timed match: two teams, score tracking, kickoff resets after each goal.
-# The opponent ship is currently inert (base ShipController, zero action) —
-# it becomes the AI opponent once an AIShipController exists (see TODO.md),
-# and additional player ships once multiplayer lands.
+# The opponent is a trained AI bot when a policy model is configured
+# (see TRAINING.md for training and promoting models into res://bots/),
+# otherwise an inert placeholder ship.
 
 signal timer_updated(minutes: int, seconds: int)
 signal score_changed(score: Dictionary)
 
 @export var match_length_seconds := 150.0
 
+@export_group("AI opponent")
+# Trained policy for the opponent; empty = inert placeholder ship.
+@export_file("*.json") var bot_model_path: String = ""
+# Difficulty handicaps, applied on top of the model (see AIShipController).
+@export_range(1, 60) var bot_reaction_ticks: int = 8
+@export_range(0.0, 1.0) var bot_action_noise: float = 0.0
+
 var score := {0: 0, 1: 0}
 var match_timer: Timer
 
@@ -18,7 +25,7 @@ func _start() -> void:
 	spawn_ball()
 	var player_ship := spawn_ship(0, 0, PlayerShipController.new())
 	spawn_camera_rig(player_ship)
-	spawn_ship(1, 0, ShipController.new())  # inert placeholder opponent
+	spawn_ship(1, 0, _make_opponent_controller())
 
 	match_timer = Timer.new()
 	match_timer.one_shot = true
@@ -28,6 +35,18 @@ func _start() -> void:
 	match_timer.start()
 
 
+func _make_opponent_controller() -> ShipController:
+	if not bot_model_path.is_empty() and FileAccess.file_exists(bot_model_path):
+		var bot := AIShipController.new()
+		bot.model_path = bot_model_path
+		bot.reaction_ticks = bot_reaction_ticks
+		bot.action_noise = bot_action_noise
+		return bot
+	if not bot_model_path.is_empty():
+		push_warning("MatchMode: bot model not found at %s, spawning inert opponent" % bot_model_path)
+	return ShipController.new()  # inert placeholder
+
+
 func _process(_delta):
 	if match_timer and match_timer.time_left > 0:
 		var remaining := ceili(match_timer.time_left)