Improve readability and randomize guest landing pet.

Pair Share Tech Mono body text with Press Start 2P display accents, and show a randomized dressed pixel character for signed-out homepage previews.

components/layout/site-header.tsx

@@ -11,7 +11,7 @@ export function SiteHeader() {
   return (
     <header className="w-full border-b border-b-foreground/10">
       <div className="mx-auto flex h-16 w-full max-w-5xl items-center justify-between px-5 text-sm">
-        <Link href={routes.home} className="font-semibold tracking-tight">
+        <Link href={routes.home} className="font-pixel text-xs tracking-tight">
           Habit Pet
         </Link>
         {!hasEnvVars ? (