feat: stealth mode — replace game-related text with discrete symbols

Replace "Game Lobby", "Connect 4", and "Snake" headings with colored
circles (●●●●) and tildes (~~~~) so the UI is less obviously a game
at a glance. Also neutralize the lobby description text and shorten
the back link.

main.go

@@ -483,7 +483,7 @@ func main() {
 			var content []h.H
 			content = append(content,
 				ui.BackToLobby(),
-				h.H1(h.Class("text-3xl font-bold"), h.Text("Connect 4")),
+				ui.StealthTitle("text-3xl font-bold"),
 				ui.PlayerInfo(g, myColor),
 				ui.StatusBanner(g, myColor, createRematch.OnClick()),
 				ui.BoardComponent(g, columnClick, myColor),
@@ -674,7 +674,7 @@ func main() {
 			var content []h.H
 			content = append(content,
 				ui.BackToLobby(),
-				h.H1(h.Class("text-3xl font-bold"), h.Text("Snake")),
+				h.H1(h.Class("text-3xl font-bold"), h.Text("~~~~")),
 				ui.SnakePlayerList(sg, mySlot),
 				ui.SnakeStatusBanner(sg, mySlot, createRematch.OnClick()),
 			)