Update via to v0.4.0 and decouple tick rate from snake speed

Use via.OnKeyDownMap for snake keybindings, replacing the manual
dataExpr/rawDataAttr workaround. Window-scoped key handling removes
the need for tabindex/focus hacks, and WithPreventDefault on arrow
keys prevents page scrolling during gameplay.

Introduce a 60 FPS tick loop with a separate snake movement speed
(7 cells/s) so direction input is polled every frame but game state
only advances at the configured rate.

snake/loop.go

@@ -5,7 +5,10 @@ import (
 )
 
 const (
-	tickInterval     = 500 * time.Millisecond
+	targetFPS        = 60
+	tickInterval     = time.Second / targetFPS
+	snakeSpeed       = 7 // cells per second
+	moveInterval     = time.Second / snakeSpeed
 	countdownSeconds = 10
 	inactivityLimit  = 60 * time.Second
 )
@@ -91,6 +94,7 @@ func (si *SnakeGameInstance) gamePhase() {
 	defer ticker.Stop()
 
 	lastInput := time.Now()
+	var moveAccum time.Duration
 
 	for {
 		select {
@@ -104,7 +108,7 @@ func (si *SnakeGameInstance) gamePhase() {
 				return
 			}
 
-			// Apply pending directions (iterate all 8 slots)
+			// Apply pending directions every tick for responsive input
 			inputReceived := false
 			for i := 0; i < 8; i++ {
 				if si.pendingDir[i] != nil && i < len(si.game.State.Snakes) && si.game.State.Snakes[i] != nil {
@@ -128,6 +132,14 @@ func (si *SnakeGameInstance) gamePhase() {
 				return
 			}
 
+			// Only advance game state at snakeSpeed
+			moveAccum += tickInterval
+			if moveAccum < moveInterval {
+				si.gameMu.Unlock()
+				continue
+			}
+			moveAccum -= moveInterval
+
 			state := si.game.State
 
 			// Advance snakes