fix: remove hard-coded car count from game loop

The useSteamJourney hook was still using hard-coded MAX_CARS = 5 for:
- Checking which cars should board passengers
- Checking which cars should deliver passengers
- Calculating when entire train exits (route completion)

This caused the game to wait for a 5-car train to exit even when there were
fewer passengers, making players answer problems well after the last visible
car had exited.

Now dynamically calculates maxCars in the game loop using the same
calculateMaxConcurrentPassengers() utility, ensuring route completion
happens as soon as the actual last car exits.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

apps/web/src/app/games/complement-race/hooks/useSteamJourney.ts

@@ -1,6 +1,6 @@
-import { useEffect, useRef } from 'react'
+import { useEffect, useRef, useMemo } from 'react'
 import { useComplementRace } from '../context/ComplementRaceContext'
-import { generatePassengers } from '../lib/passengerGenerator'
+import { generatePassengers, calculateMaxConcurrentPassengers } from '../lib/passengerGenerator'
 import { useSoundEffects } from './useSoundEffects'
 
 /**
@@ -103,7 +103,8 @@ export function useSteamJourney() {
       // Check for passengers that should board
       // Passengers board when an EMPTY car reaches their station
       const CAR_SPACING = 7 // Must match SteamTrainJourney component
-      const MAX_CARS = 5
+      const maxPassengers = calculateMaxConcurrentPassengers(state.passengers, state.stations)
+      const maxCars = Math.max(1, maxPassengers)
       const currentBoardedPassengers = state.passengers.filter(p => p.isBoarded && !p.isDelivered)
 
       // Find waiting passengers whose origin station has an empty car nearby
@@ -115,7 +116,7 @@ export function useSteamJourney() {
 
         // Check if any empty car is at this station
         // Cars are at positions: trainPosition - 7, trainPosition - 14, etc.
-        for (let carIndex = 0; carIndex < MAX_CARS; carIndex++) {
+        for (let carIndex = 0; carIndex < maxCars; carIndex++) {
           // Skip if this car already has a passenger
           if (currentBoardedPassengers[carIndex]) continue
 
@@ -157,9 +158,9 @@ export function useSteamJourney() {
       })
 
       // Check for route completion (entire train exits tunnel)
-      // With 5 cars at 7% spacing, last car is at trainPosition - 35%
-      // So wait until trainPosition >= 135% for entire train to exit
-      const ENTIRE_TRAIN_EXIT_THRESHOLD = 100 + (MAX_CARS * CAR_SPACING) // 135%
+      // Last car is at trainPosition - (maxCars * CAR_SPACING)%
+      // So wait until trainPosition >= 100 + (maxCars * CAR_SPACING)% for entire train to exit
+      const ENTIRE_TRAIN_EXIT_THRESHOLD = 100 + (maxCars * CAR_SPACING)
 
       if (trainPosition >= ENTIRE_TRAIN_EXIT_THRESHOLD && state.trainPosition < ENTIRE_TRAIN_EXIT_THRESHOLD) {
         // Play celebration whistle