Consistency sweep: fix switcher layout, gaps, buttons, empty states

- Home: mode switcher moved to its own row (no longer crammed next to
  title on mobile), hide-watched simplified to text-only toggle
- Home/History/Discovery: pagination buttons text-sm → text-xs, page
  counter text-sm → text-xs
- Liked/Downloads/SearchResults: top-level gap-8 → gap-6
- Liked: refresh button px-4 py-2 text-sm → px-3 py-1.5 text-xs
- Empty states: standardize to text-zinc-500 text-sm across Queue,
  ContinueWatching, History, Following, Discovery, Liked
- Following: "Latest uploads" tab label → "Feed"
- Home: remove -mt-3 hacks from mode description rows

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

frontend/src/pages/SearchResults.jsx

@@ -68,7 +68,7 @@ export default function SearchResults() {
   const channelsFirst = channels.length > 0 && (videos.length === 0 || source === "local");
 
   return (
-    <div className="flex flex-col gap-8">
+    <div className="flex flex-col gap-6">
       <div className="flex items-center gap-3 flex-wrap">
         <h1 className="font-display font-semibold text-xl text-zinc-100">
           Results for <span className="text-accent">"{q}"</span>