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.

assets/css/input.css

@@ -3,7 +3,7 @@
 @source not "./daisyui{,*}.mjs";
 @plugin "./daisyui.mjs";
 @plugin "./daisyui-theme.mjs" {
-  name: "connect4";
+  name: "stealth";
   default: true;
   color-scheme: light;