UX: list view everywhere, mobile polish, affinity dismissal fix

- Default list view across all pages (Home, Following, History, Queue,
  ContinueWatching, Liked, Discovery, SearchResults, Channel)
- Watch.jsx mobile: smaller chips/title/avatar/meta, hide tags + keyboard
  hint on mobile, tighter gaps, compact description padding
- Fix mobile bottom nav showing focus outline on tap
- Fix _update_affinity to write negative entries (not just positive) so
  dislikes/dismissals on unseen content actually register
- Dismissing a discovery video now fires -3.0 affinity against its tags,
  matching the dislike weight

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

frontend/src/pages/Home.jsx

@@ -21,7 +21,7 @@ export default function Home() {
   const [dismissed, setDismissed] = useState(new Set());
   const [shuffleKey, setShuffleKey] = useState(0);
   const [duration, setDuration] = useState("");
-  const [viewMode, setViewMode] = useState(() => localStorage.getItem("home-view-mode") ?? "grid");
+  const [viewMode, setViewMode] = useState(() => localStorage.getItem("home-view-mode") ?? "list");
 
   const toggleViewMode = () => {
     const next = viewMode === "grid" ? "list" : "grid";