Drive the Lambos and Ferraris in the garage (#43)

[webdevcody]

Closes #43.

Walk up to any of the nine cars in the garage (or the Lambo parked out front) and press E to get behind the wheel. W is the gas, S brakes and then reverses, A/D steer, Space brakes, H honks, E gets you out. Press E at a car someone else is driving to ride in the passenger seat.

How it works

• Physics runs on the driver's page (shared/garage.ts): an arcade bicycle model (0 to 20 m/s, tighter turns at a crawl than flat out), moved in ≤25 cm steps so nothing thin gets skipped. Cars stay on the pavement: the garage, the lot in front, the east lot, across the sidewalk and ±90 m along the street. Columns, walls, lamp posts, tree trunks (they get colliders now) and other cars stop you. Hit something head on and you bounce off with a crunch. Hit it at an angle and you slide along it and turn parallel. A car that drives into someone standing on the street knocks them aside.
• The office keeps seats and positions (server/garage.ts, one per floor like the basketball court): one driver and one passenger per car. Only the driver's car.drive moves a car. Poses off the pavement are ignored, and speed and steering are clamped. Nothing is saved, so a restart parks every car back in its spot. A car you get out of (or disconnect from, or leave by elevator) stays where you left it.
• Everyone on the floor sees it: drives are relayed at ~15 Hz. Other pages smooth them and extrapolate up to 0.25 s. The roof comes off while anyone's in a car (windshield, bucket seats, steering wheel), so you can see who's driving. The front wheels steer, and the name tag says "🏎️ driving the Orange Lambo" or "riding in…" (in the people list too). There's a positional engine note with fake gear shifts, plus the horn, doors and crashes.
• Races: the office answers each of your own car.enter/car.leave with answer: true. The page only reconciles once all of its own requests are answered, so someone else's car news arriving mid-request can't kick you out. If someone did beat you to the seat, you're put out with a toast.
• Edge cases: riding the elevator, switching floors, N to a desk and walk-to all get you out first. A reload mid-drive puts you back on your feet beside the car, and the tab's pagehide parks the car exactly where you were. On a reconnect you get back into your seat if it's still free.
• Cost: each car is now its own set of meshes (the old garage merged all nine into one batch). Up in the office, cars fully under the building aren't drawn, so the office view's draw calls are unchanged: 1733 with the fleet vs 1778 hidden, which is noise. In the garage and on the street they add ~185–300 calls. Headless Metal Chrome stayed at 60 fps everywhere.

Docs: docs/controls.md (W A S D, Space, E, and a new H row), docs/features.md, and the in-game help (H).

Testing

• npm run typecheck, and npm test: 299 pass, including the new tests/garage.test.ts (roster/pavement/physics/SAT overlap, server seats/drive validation/honk rate) and tests/driving.test.ts (a real Fleet + Driver: drives down the road, stops at a column with a crunch and reverses away, slides along an angled wall and lines up with it, gets out by the driver's door or not at all when boxed in, passenger can't drive).
• Headless Chrome smokes against a real office, two or three pages at once:
  • Ann and Bob each get into a Ferrari, drive out of the garage and along the street in opposite directions. Once stopped, both pages agree on both cars' positions, and each draws the other sitting in their car.
  • Bob's page shows "🏎️ driving the Rosso Ferrari". Ann's honk is heard on Bob's page. When Ann gets out, the car stays parked for Bob.
  • Bob rides with Ann in the Blue Lambo and moves with the car. Cat sees "Ann and Bob · full". Driving head on into a garage column stops the car with a crunch. Driving at Bob on foot knocks him ~1.3 m to the side. Ann riding the elevator to the roof mid-drive leaves the car parked and free.
  • An office restart parks the moved car back at its spot. On a two-floor building, driving from the upper floor's garage (street at y −10.7) works, and a reload mid-drive puts you beside your car.

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