Compact all mode/tab switchers site-wide

Home feed mode: px-3 py-1.5 text-sm → px-2 py-1 text-xs, tighter container
Hide-watched toggle: same reduction
Following tabs: px-4 py-2 text-sm → px-3 py-1.5 text-xs, "Latest uploads" → "Feed"
Discovery tabs: same reduction

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/pages/Discovery.jsx

@@ -176,7 +176,7 @@ function Tab({ active, onClick, children, count }) {
     <button
       onClick={onClick}
       className={[
-        "px-4 py-2 text-sm font-medium border-b-2 transition-colors -mb-px flex items-center gap-2",
+        "px-3 py-1.5 text-xs font-medium border-b-2 transition-colors -mb-px flex items-center gap-1.5",
         active
           ? "border-accent text-zinc-100"
           : "border-transparent text-zinc-500 hover:text-zinc-300",