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/components/Layout.jsx

@@ -40,7 +40,7 @@ function BottomNav({ newCount }) {
             to={tab.to}
             end={tab.end}
             className={({ isActive }) =>
-              `relative flex-1 flex flex-col items-center justify-center gap-0.5 transition-colors ${
+              `relative flex-1 flex flex-col items-center justify-center gap-0.5 transition-colors outline-none ${
                 isActive ? "text-accent" : "text-zinc-500"
               }`
             }