fix(complement-race): train now moves in sprint mode

**THE BUG**: Validator was only updating momentum in Sprint mode,
but NEVER updating position! This caused trainPosition to stay at 0.

**THE FIX**: Added position calculation based on momentum:
- moveDistance = momentum / 20
- Starting momentum (50) → 2.5 units per answer
- Max momentum (100) → 5 units per answer
- Creates progression: higher momentum = faster train movement

Position updates per answer now work:
- Correct answer: momentum +15, then position +=(momentum/20)
- Wrong answer: momentum -10, then position +=(momentum/20)
- Position capped at 100 (end of route)

This matches the original single-player behavior where the train
speed was tied to momentum.

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

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

apps/web/src/app/arcade/complement-race/components/RaceTrack/SteamTrainJourney.tsx

@@ -94,7 +94,9 @@ export function SteamTrainJourney({
   currentInput,
 }: SteamTrainJourneyProps) {
   const { state } = useComplementRace()
-  console.log(`🚂 Train: mom=${momentum} pos=${trainPosition} stations=${state.stations.length} passengers=${state.passengers.length}`)
+  console.log(
+    `🚂 Train: mom=${momentum} pos=${trainPosition} stations=${state.stations.length} passengers=${state.passengers.length}`
+  )
 
   const { getSkyGradient, getTimeOfDayPeriod } = useSteamJourney()
   const _skyGradient = getSkyGradient()

apps/web/src/arcade-games/complement-race/Provider.tsx

@@ -330,7 +330,9 @@ export function ComplementRaceProvider({ children }: { children: ReactNode }) {
     }
   }, [multiplayerState, localPlayerId, localUIState])
 
-  console.log(`🚂 Sprint: momentum=${compatibleState.momentum} pos=${compatibleState.trainPosition} pressure=${compatibleState.pressure}`)
+  console.log(
+    `🚂 Sprint: momentum=${compatibleState.momentum} pos=${compatibleState.trainPosition} pressure=${compatibleState.pressure}`
+  )
 
   // Action creators
   const startGame = useCallback(() => {

apps/web/src/arcade-games/complement-race/Validator.ts

@@ -317,12 +317,17 @@ export class ComplementRaceValidator
         updatedPlayer.position = Math.min(100, player.position + 100 / state.config.raceGoal)
       }
     } else if (state.config.style === 'sprint') {
-      // Sprint: Update momentum
+      // Sprint: Update momentum AND position
       if (correct) {
         updatedPlayer.momentum = Math.min(100, player.momentum + 15)
       } else {
         updatedPlayer.momentum = Math.max(0, player.momentum - 10)
       }
+
+      // Move train based on momentum (momentum/20 = position change per answer)
+      // Higher momentum = faster movement
+      const moveDistance = updatedPlayer.momentum / 20
+      updatedPlayer.position = Math.min(100, player.position + moveDistance)
     } else if (state.config.style === 'survival') {
       // Survival: Always move forward, speed based on accuracy
       const moveDistance = correct ? 5 : 2