feat(*): add wall/ceiling surface pull and retune ball-ship materials

Game/scripts/ship.gd

@@ -19,6 +19,12 @@ extends RigidBody3D
 @export var drag_coefficient = 0.98      # Linear drag (air resistance)
 @export var angular_drag = 0.95          # Rotational drag
 
+@export_group("Surface Pull")
+@export var wall_pull_strength = 6.0     # Wall grav-plating strength (m/s^2-equivalent)
+@export var wall_pull_range = 3.0        # Metres from a wall where pull begins
+@export var ceiling_pull_strength = 11.5 # Ceiling grav-plating strength; nets above gravity so a ship can hold a ceiling
+@export var ceiling_pull_range = 3.0     # Metres from the ceiling where pull begins
+
 # Accent colours per team, applied to the nose and tail fin meshes so the
 # two sides are tellable apart at a glance.
 const TEAM_COLORS := {
@@ -34,6 +40,7 @@ var team: int = 0:
 
 var controller: ShipController
 var _current_action: ShipAction = ShipAction.new()
+var _boundary: ArenaBoundary
 
 # Instrument signals for efficient data distribution
 signal speed_changed(speed: float)
@@ -74,6 +81,8 @@ func _ready():
 
 	_apply_team_color()
 
+	_boundary = get_tree().get_first_node_in_group("arena_boundary")
+
 
 func _apply_team_color() -> void:
 	if not is_inside_tree():
@@ -112,6 +121,7 @@ func _integrate_forces(state):
 
 	# === TRANSLATION (Movement) ===
 	apply_thruster_forces(state, _current_action)
+	apply_surface_pull(state)
 
 	# === ROTATION (Turning) ===
 	apply_rotation_forces(state, _current_action.rotation)
@@ -153,6 +163,16 @@ func apply_thruster_forces(state: PhysicsDirectBodyState3D, action: ShipAction):
 	state.apply_central_force(world_thrust)
 
 
+func apply_surface_pull(state: PhysicsDirectBodyState3D) -> void:
+	if _boundary == null:
+		return
+	var pull := _boundary.get_surface_pull(
+		global_position, wall_pull_strength, wall_pull_range,
+		ceiling_pull_strength, ceiling_pull_range
+	)
+	state.apply_central_force(pull * mass)
+
+
 func apply_rotation_forces(state: PhysicsDirectBodyState3D, rotation_input: Vector3):
 	if rotation_input.length() < 0.01:
 		return