refactor(team-colors): collapse disagreeing team palettes into one source of truth

ship.gd, HUDController.gd, and goal.gd each declared their own TEAM_COLORS,
arena_boundary.gd/arena_deck.gdshader had a third pair, and HUD.tscn baked
in a fourth (hardcoded "BLUE"/"ORANGE" labels) — nose, goal rim, end zone,
and scoreboard all rendered different blues. New scripts/team_colors.gd
(class_name TeamColors) is now the single source every one of those reads
from, and team identity moves to purple/green.

Game/scripts/ship.gd

@@ -25,13 +25,6 @@ extends RigidBody3D
 @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 := {
-	0: Color(0.25, 0.55, 1.0),
-	1: Color(1.0, 0.5, 0.15),
-}
-
 # Non-tinted hull meshes, runtime-merged into one ArrayMesh by
 # _build_merged_hull() (Nose/TailFin stay separate MeshInstance3Ds since
 # _apply_team_color() retints them per-team and must keep addressing them by
@@ -73,7 +66,7 @@ static var _team_materials: Dictionary = {}  # team:int -> StandardMaterial3D
 static func _get_team_material(team: int) -> StandardMaterial3D:
 	if _team_materials.has(team):
 		return _team_materials[team]
-	var color: Color = TEAM_COLORS.get(team, TEAM_COLORS[0])
+	var color: Color = TeamColors.TEAM_COLORS.get(team, TeamColors.TEAM_COLORS[0])
 	var accent := StandardMaterial3D.new()
 	accent.albedo_color = color
 	accent.metallic = 0.3