Scope cut: drive-only MVP (remove racing + economy)

Per user direction, the MVP is now simply driving cars on the expressway.
- Removed RaceManager and Economy modules entirely
- Slimmed Remotes to DataUpdated / SpawnCar / EquipCar
- ProfileTemplate now just remembers the last driven car (v2)
- Cars: dropped price/rep/upgrade fields; kept identity + driving stats
- CarManager: stat-based tuning only; RX-7 allowlist via GameConfig.canDrive
- DataManager: assign default car on join; downgrade RX-7 if de-allowlisted
- Client: replaced garage/economy UI with a simple car picker + respawn
- Docs: GDD/ROADMAP/README rewritten for drive-only; added docs/MESH_SWAP.md
- Gates: stylua clean, selene 0/0, rojo builds

docs/MESH_SWAP.md

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+# Swapping the placeholder RX-7 for the real mesh (M1)
+
+Right now every car is a coloured block + a `VehicleSeat` so the game is drivable
+today. This is the **one file** you touch to make the RX-7 a real model:
+`src/server/CarManager.luau` → the `buildCarModel` function.
+
+Nothing else (saving, the allowlist, car switching, the map, anti-cheat) needs to
+change. That's the whole point of isolating model-building in one function.
+
+## Reference photos
+The real car's reference photos live on the NAS (too large to commit to git):
+
+```
+unraid-1:/mnt/user/data/yy-roblox-games/0-fast-n-furious-sim/001-1993 Mazda RX-7/
+```
+
+A single downscaled reference is included at `assets/reference/rx7-reference.png`
+for quick lookups.
+
+## Step 1 — Get a model into Roblox
+Options, easiest first:
+1. **Buy or find a free RX-7 FD model** on the Roblox Creator Marketplace/toolbox,
+   or
+2. **Model it** in Blender from the reference photos and import the mesh
+   (`.fbx`/`.obj`) via Studio's 3D importer, or
+3. Commission one.
+
+You want a single `Model` whose parts are welded together, with a clear "body"
+part you can drive. Keep the part count low (mobile perf).
+
+## Step 2 — Store it where Rojo/Studio can clone it
+Put the finished `Model` under `ReplicatedStorage` (e.g. a `CarModels` folder).
+Two ways to manage it:
+- **Simple:** keep it in the Studio place file as a real Instance (not synced by
+  Rojo). Fine for a single hero car.
+- **Version-controlled:** export the model to a `.rbxm` and reference it from the
+  Rojo project so it lives in git. See Rojo's `$path` docs for `.rbxm` model files.
+
+## Step 3 — Rewrite `buildCarModel` to clone the real mesh
+Replace the block-building body of `buildCarModel(car, maxSpeed, torque, turnSpeed)`
+with something like:
+
+```lua
+local CAR_MODELS = ReplicatedStorage:WaitForChild("CarModels")
+
+local function buildCarModel(car, maxSpeed, torque, turnSpeed)
+    -- Look up a real model by car id; fall back to the block builder if missing.
+    local template = CAR_MODELS:FindFirstChild(car.Id)
+    if not template then
+        return buildBlockCar(car, maxSpeed, torque, turnSpeed) -- keep the old code as a fallback
+    end
+
+    local model = template:Clone()
+
+    -- Ensure it has a VehicleSeat named "DriveSeat" welded to the driving body.
+    local seat = model:FindFirstChild("DriveSeat")
+    if not seat then
+        seat = Instance.new("VehicleSeat")
+        seat.Name = "DriveSeat"
+        -- weld seat to model.PrimaryPart, position it in the cabin...
+        seat.Parent = model
+    end
+    seat.MaxSpeed = maxSpeed
+    seat.Torque = torque
+    seat.TurnSpeed = turnSpeed
+
+    assert(model.PrimaryPart, "Car model needs a PrimaryPart set")
+    return model
+end
+```
+
+Keep the current block-builder renamed as `buildBlockCar` so any car without a
+real mesh still works. That way you can import cars one at a time.
+
+## Step 4 (recommended, M1) — Move to a real chassis
+The `VehicleSeat` is great for "it drives today" but for real suspension/grip,
+adopt a proven **constraint chassis** (A-Chassis or a modern equivalent). At that
+point `buildCarModel` clones the chassis rig and attaches the RX-7 body to it.
+Still one function; still no changes elsewhere.
+
+## Verify
+- `rojo build --output build.rbxl` compiles.
+- In Studio: Play → you spawn in the real RX-7 → it drives → it saves.
+- Non-allowlisted test account still can't select the RX-7 (server enforced).