feat: implement obstacle manager for randomized static wall spawning, integrate into main scene, and add stop-n-go manager.

scenes/main.gd

@@ -11,6 +11,7 @@ var screen_shake_manager
 var touch_controls
 var camera_context_manager
 var stop_n_go_manager
+var obstacle_manager
 
 # Minimal local state
 var _connection_check_timer: float = 0.0
@@ -117,6 +118,12 @@ func _init_managers():
 	add_child(camera_context_manager)
 	camera_context_manager.initialize($Camera3D200, screen_shake_manager)
 	
+	# Obstacle manager for dynamic walls
+	obstacle_manager = load("res://scripts/managers/obstacle_manager.gd").new()
+	obstacle_manager.name = "ObstacleManager"
+	add_child(obstacle_manager)
+	obstacle_manager.initialize(self, $EnhancedGridMap)
+	
 	# Connect signals for UI updates
 	goals_cycle_manager.timer_updated.connect(_on_timer_updated)
 	goals_cycle_manager.score_updated.connect(_on_score_updated)
@@ -591,6 +598,14 @@ func _start_game():
 		_assign_random_spawn_positions()
 		
 		# PRE-GAME COUNTDOWN (3s)
+		# Spawn static obstacles before countdown starts
+		if obstacle_manager:
+			obstacle_manager.spawn_random_obstacles(15)
+			
+		# Spawn mission tiles BEFORE countdown but AFTER walls (Stop n Go only)
+		if LobbyManager.game_mode == "Stop n Go" and stop_n_go_manager:
+			stop_n_go_manager.setup_mission_tiles()
+			
 		await _start_pre_game_countdown()
 		
 		GameStateManager.start_game()
@@ -623,6 +638,7 @@ func _start_game():
 
 		# Spawn Tekton NPC
 		spawn_tekton_npc()
+		
 
 func _assign_random_spawn_positions():
 	"""Assign spawn positions distributed to 4 corners (2 per corner for 8 players)."""