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/article/ArticleView.tsx

@@ -306,7 +306,7 @@ export function ArticleView() {
             value={commentText}
             onChange={(e) => { setCommentText(e.target.value); autoResize(e); }}
             onKeyDown={(e) => { if (e.key === "Enter" && !e.shiftKey) { e.preventDefault(); handleComment(); } }}
-            placeholder="Write a comment about this article..."
+            placeholder="Write a comment…"
             rows={3}
             className="w-full bg-bg-raised border border-border rounded-sm px-3 py-2 text-[12px] text-text placeholder:text-text-dim resize-none focus:outline-none focus:border-accent leading-relaxed"
             autoFocus