feat: add glowing effect to active player's pieces

Pulsing box-shadow on the current turn's placed pieces makes the
turn state visible directly on the board rather than only in the
status banner.

ui/board.go

@@ -11,12 +11,18 @@ type ColumnClickFn func(col int) h.H
 func BoardComponent(g *game.Game, columnClick ColumnClickFn, myColor int) h.H {
 	var cols []h.H
 
+	activeTurn := 0
+	if g.Status == game.StatusInProgress {
+		activeTurn = g.CurrentTurn
+	}
+
 	for col := 0; col < 7; col++ {
 		var cells []h.H
 		for row := 0; row < 6; row++ {
 			cellColor := g.Board[row][col]
 			isWinning := g.IsWinningCell(row, col)
-			cells = append(cells, Cell(cellColor, isWinning))
+			isActiveTurn := cellColor != 0 && cellColor == activeTurn
+			cells = append(cells, Cell(cellColor, isWinning, isActiveTurn))
 		}
 
 		// Column is clickable only if it's player's turn and game is in progress
@@ -45,7 +51,7 @@ func Column(colIdx int, cells []h.H, columnClick ColumnClickFn, canClick bool) h
 	return h.Div(attrs...)
 }
 
-func Cell(color int, isWinning bool) h.H {
+func Cell(color int, isWinning, isActiveTurn bool) h.H {
 	class := "cell"
 	switch color {
 	case 1:
@@ -56,5 +62,8 @@ func Cell(color int, isWinning bool) h.H {
 	if isWinning {
 		class += " winning"
 	}
+	if isActiveTurn {
+		class += " active-turn"
+	}
 	return h.Div(h.Class(class))
 }