Add Connect 4 multiplayer game server

Real-time two-player Connect 4 using Via framework with:
- Game creation and invite links
- SSE-based live updates for both players
- Win detection with animated highlighting
- Session-based nickname persistence

game/types.go

@@ -0,0 +1,41 @@
+package game
+
+import "time"
+
+type PlayerID string
+
+type Player struct {
+	ID       PlayerID
+	Nickname string
+	Color    int // 1 = Red, 2 = Yellow
+}
+
+type GameStatus int
+
+const (
+	StatusWaitingForPlayer GameStatus = iota
+	StatusInProgress
+	StatusWon
+	StatusDraw
+)
+
+type Game struct {
+	ID           string
+	Board        [6][7]int  // 6 rows, 7 columns; 0=empty, 1=red, 2=yellow
+	Players      [2]*Player // Index 0 = creator (Red), Index 1 = joiner (Yellow)
+	CurrentTurn  int        // 1 or 2 (matches player color)
+	Status       GameStatus
+	Winner       *Player
+	WinningCells [][2]int // Coordinates of winning 4 cells for highlighting
+	CreatedAt    time.Time
+}
+
+func NewGame(id string) *Game {
+	return &Game{
+		ID:          id,
+		Board:       [6][7]int{},
+		CurrentTurn: 1, // Red goes first
+		Status:      StatusWaitingForPlayer,
+		CreatedAt:   time.Now(),
+	}
+}