[WIP] Add option for two players in the menu

[Copilot]

• Add twoPlayer flag and P2 state fields to resetGameState()
• Update getCharOrder() to handle 2P mode (P2 is truck index 1, not AI)
• Add "2 PLAYERS" menu item to MainMenuScene + update _select() + update controls panel
• Update PlayerSelectScene to support simultaneous character selection for P2 (WASD/ZQSD + F to confirm)
• Update RaceScene:
  • Mark truck[1] as isP2 in 2P mode
  • Set up P2 keyboard (W/Z, A/Q, S, D, F)
  • Add drivePlayer2() method using P2 keys
  • Camera follow midpoint of P1+P2 on big tracks
  • checkPks() updates P2 money/nitros
  • HUD shows P2 nitro
  • End race waits for both players
  • endRace() saves P2 prize and stats
• Update ResultsScene to mark P1 and P2 in results
• Update ShopScene for simultaneous 2P upgrade selection (P1: 1-5+ENTER, P2: 6-0+F)

Original prompt

Add an option for 2 players in the menu. Player two controls are WASD or ZQSD AZERTY keyboard folks. F is the Nitro button. At the end of the race, they can both choose their upgrades at the same time.

Created from Copilot CLI via the copilot delegate command.