chore(multiplayer): Phase 0 refactors + graphics/perf settings groundwork

Lands the non-networked Phase 0 tasks from multiplayer-todo.md (ship/camera/
arena refactors, sim constants, background FPS handling) plus a first pass
at exposing graphics/performance settings (presets, resolution scaling,
vsync, FPS cap, perf overlay) and a GPU profiling harness for the
real-hardware follow-up in task 0.15b.

Game/objects/ball.tscn

@@ -15,6 +15,7 @@ collision_mask = 13
 mass = 3
 physics_material_override = SubResource("PhysicsMaterial_ball")
 continuous_cd = true
+can_sleep = false
 inertia = Vector3(3, 3, 3)
 gravity_scale = 0.8
 linear_damp = 0.1