fix(profile): visual frame previews in shop + sidebar avatar sync

Shop items of type 'frame' now render a real avatar-sized preview with
the frame's CSS applied (instead of a generic lucide icon) so buyers
see exactly what they're paying for. Title items get a tag-shaped
preview in their color. The avatar-frames section above the shop also
shows the user's actual avatar inside the frame circles, not 'LS' text.

Sidebar nav-avatar now:
  • renders the uploaded avatar_url instead of always showing initials
    (LS.initPage + new LS.refreshNavAvatar helper)
  • picks up frame CSS on every page via applyCosmetics — previously
    only dashboard.html applied it
  • repaints immediately after picking/deleting an avatar preset
    (avPickPreset / avDelete now call LS.setUser + LS.refreshNavAvatar)

Backend getMyActive resolves avatar_frame to {id, css} for both
gamification frames ('fire', 'crown', ...) and shop-purchased frames
('shop_<id>'), so the client doesn't need a second round-trip to
look up the CSS.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/css/ls.css

@@ -494,6 +494,7 @@ body {
   font-family: 'Unbounded', sans-serif;
   font-size: 0.6rem; font-weight: 800; color: #fff;
   flex-shrink: 0;
+  overflow: hidden;
 }
 
 .sb-user-info { flex: 1; min-width: 0; }