fix: empty 3x3 tiles below candy cannon and add outline shaders to cannon, projectiles, bubbles and vfx

scripts/managers/gauntlet_manager.gd

@@ -412,11 +412,11 @@ func _apply_arena_setup() -> void:
 			var pos = Vector2i(x, z)
 			
 			# Center 3x3 block: NPC obstacle (Candy Pump)
-			if _is_npc_zone(pos):
-				# Make the floor walkable visually instead of obstacle red
-				gridmap.set_cell_item(Vector3i(x, 0, z), TILE_WALKABLE)
-				gridmap.set_cell_item(Vector3i(x, 1, z), -1)
-				continue
+				if _is_npc_zone(pos):
+					# Make the floor empty (-1) beneath the Candy Pump
+					gridmap.set_cell_item(Vector3i(x, 0, z), -1)
+					gridmap.set_cell_item(Vector3i(x, 1, z), -1)
+					continue
 			
 			# Boundary walls: perimeter (row 0, row 19, col 0, col 19)
 			if x == 0 or x == ARENA_COLUMNS - 1 or z == 0 or z == ARENA_ROWS - 1:
@@ -982,6 +982,12 @@ func _spawn_impact_particles(targets: Array) -> void:
 		spatial_mat.emission_enabled = true
 		spatial_mat.emission = Color(1.0, 0.6, 0.8)
 		spatial_mat.emission_energy_multiplier = 2.0
+		
+		# Outline shader for splash VFX
+		var outline_mat = ShaderMaterial.new()
+		outline_mat.shader = load("res://assets/shaders/outline3d.gdshader")
+		spatial_mat.next_pass = outline_mat
+		
 		mesh.material = spatial_mat
 		particles.draw_pass_1 = mesh
 
@@ -1558,6 +1564,11 @@ func _spawn_bubble_visual(center: Vector2i) -> void:
 	mat.emission_enabled = true
 	mat.emission = Color(1.0, 0.2, 0.6)
 	mat.emission_energy_multiplier = 1.5
+	
+	var outline_mat = ShaderMaterial.new()
+	outline_mat.shader = load("res://assets/shaders/outline3d.gdshader")
+	mat.next_pass = outline_mat
+	
 	mesh_inst.material_override = mat
 
 	var main = get_node_or_null("/root/Main")