Polish pass — consistency, a11y, theme correctness

- Fix bg-white toggle thumbs in Settings (broke on dark themes)
- Eliminate 2px layout shift when switching Media feed tabs
- Unify "Follow"/"Mute" capitalization in NoteCard context menu
- Replace ASCII "..." with unicode ellipsis across compose/search/article
- Add rounded-sm to dropdowns, emoji picker, post/reply buttons
- Add aria-labels to sidebar toggle and onboarding copy buttons
- Add role=tablist/tab/aria-selected to login mode tabs
- Replace inline width/height styles with Tailwind w-16 h-16 in ProfileView
- Replace inline transform style with rotate-90 class in SettingsView
- Unify sidebar active state opacity (bg-accent/8 → bg-accent/10)
- Pad sidebar badges with py-0.5 for consistent pill height
- Match thread reply button sizing to compose post button
- Use var(--font-reading) on non-zen article title for consistency
- Format 'saved Xs ago' as minutes/hours after 60s
- Unify expand chevron to ▶ + rotate-90 pattern
- PollWidget: transition-all → transition-colors (no layout animation)
- Remove cryptic 'Ctrl+Enter' hint from compose and thread reply

src/components/shared/SettingsView.tsx

@@ -50,7 +50,7 @@ function MuteSection() {
         onClick={() => setExpanded(!expanded)}
         className="flex items-center gap-2 w-full text-left group"
       >
-        <span className="text-text-dim text-[10px] transition-transform" style={{ transform: expanded ? "rotate(90deg)" : "rotate(0deg)" }}>
+        <span className={`text-text-dim text-[10px] transition-transform ${expanded ? "rotate-90" : "rotate-0"}`}>
           ▶
         </span>
         <h2 className="text-text text-[11px] font-medium uppercase tracking-widest text-text-dim group-hover:text-text transition-colors">
@@ -280,7 +280,7 @@ function NotificationSection() {
               }`}
             >
               <span
-                className={`absolute top-0.5 left-0.5 w-4 h-4 rounded-full bg-white transition-transform ${
+                className={`absolute top-0.5 left-0.5 w-4 h-4 rounded-full bg-bg transition-transform ${
                   settings[key] ? "translate-x-4" : "translate-x-0"
                 }`}
               />
@@ -412,7 +412,7 @@ function ExperimentalSection() {
           }`}
         >
           <span
-            className={`absolute top-0.5 left-0.5 w-4 h-4 rounded-full bg-white transition-transform ${
+            className={`absolute top-0.5 left-0.5 w-4 h-4 rounded-full bg-bg transition-transform ${
               enabled ? "translate-x-4" : "translate-x-0"
             }`}
           />