Restrict RX-7 to allowlisted UserIds (owner + son demo lock)

- GameConfig: RX7AllowedUserIds allowlist + isRX7Allowed/starterCarFor helpers
- ProfileTemplate: no hard-coded starter; granted per-player by UserId
- DataManager: grants RX-7 to allowlisted players, public car to everyone else
- Economy.buyCar + CarManager.spawn: server-side refuse RX-7 for non-allowlisted
- Cars: RX-7 flagged Restricted; client dealership hides it from non-owners
- Gates: stylua clean, selene 0/0, rojo builds

src/shared/Cars.luau

@@ -27,6 +27,7 @@ export type Car = {
 	Color: { number }, -- {r,g,b} 0-1 for the placeholder body until real mesh exists
 	Description: string,
 	Starter: boolean?, -- true = granted free on first join
+	Restricted: boolean?, -- true = allowlist-only; hidden from dealership for others
 }
 
 local Cars = {}
@@ -44,6 +45,7 @@ Cars.List = {
 		Color = { 0.85, 0.15, 0.12 }, -- classic RX-7 red until the real mesh is imported
 		Description = "The one that started it all. A rotary-hearted FD RX-7 — light, balanced, and iconic. Your daily driver and first weapon on the expressway.",
 		Starter = true,
+		Restricted = true, -- demo-locked to the owner + son during testing
 	},
 	{
 		Id = "hatch_junk",