Map v3: Shuto Night Loop — Tokyo landmark circuit

The straight strip becomes a closed rounded-rect loop (~7,400 studs/lap)
built from centerline samples, Shuto-C1 style. Landmark zones:

- Daikoku Futo PA: drivable meet lot off the south straight (guardrail
  gap entrance), painted bays, flood-light towers, bilingual sign —
  cars now SPAWN at Daikoku like a proper meet
- Rainbow Bridge over the east straight: white suspension towers with
  beacons, cross beams, rainbow-colored rail lights
- Odaiba beyond the bridge: blocky Unicorn Gundam (glowing eyes, horn,
  pink psycho-frame strips) + 16-cabin neon ferris wheel
- Yamate-style tunnel enclosing the whole north straight
- Tokyo Tower replica (orange/white tiers, two lit decks, antenna) west
- Tatsumi PA overlook pad NE
- City-core skyline inside the loop + outer ring skipping landmark zones
- Bilingual green highway signs via SurfaceGui (JP + EN)

Gameplay contract preserved: SpawnPad/FinishLine/KillWall names intact,
kill walls hug every road edge except the Daikoku entrance.

docs/ROADMAP.md

@@ -37,9 +37,16 @@ until this is true.
 
 ## M2 — More cars + polish (still no racing)
 - [ ] Import a few more real car meshes.
-- [x] Better map v2: 3200-stud expressway with gantry arches, a neon-lit
-      tunnel, jump ramps (right lane; left stays flat), end wall, and a
-      procedural neon skyline flanking the route.
+- [x] Better map v3 — **"Shuto Night Loop"**: closed ~7,400-stud circuit
+      inspired by Tokyo's Shuto expressway, with real-Tokyo landmark zones:
+      **Daikoku Futo PA** (drivable meet lot + painted bays + light towers —
+      cars spawn here), **Rainbow Bridge** (suspension towers, rainbow rail
+      lights), **Odaiba** beyond it (blocky Unicorn Gundam statue with glowing
+      psycho-frame + giant neon ferris wheel), **Yamate-style tunnel** (north
+      straight), **Tokyo Tower** replica (west), **Tatsumi PA** overlook,
+      bilingual green highway signs (大黒PA, レインボーブリッジ, お台場, 辰巳PA),
+      city-core + outer-ring procedural skyline. Not geographically accurate —
+      a themed loop, not a map of Tokyo.
 - [x] Day/night, weather mood: `src/server/Ambience.luau` — Atmosphere haze
       catching the neon, bloom + cool color-correction post effects, and a slow
       22:00→03:00 clock drift (10-min ping-pong) so the night sky breathes.