Fix player reconnection by re-registering sync context

When an existing player reconnects to a game, their sync context
is now updated so they continue receiving real-time updates.

main.go

@@ -304,6 +304,9 @@ func main() {
 				Player: player,
 				Sync:   c,
 			})
+		} else if gameExists && gi.GetPlayerColor(playerID) != 0 {
+			// Re-register sync context for existing players on reconnect
+			gi.RegisterSync(playerID, c)
 		}
 
 		c.View(func() h.H {