Harden accessibility: ARIA roles, semantic buttons, alt text, form labels

- Replace clickable divs with semantic <button> elements (NoteCard, SearchView)
- Add role="dialog", aria-modal, aria-labelledby on all modals (Login, Quote, Zap, Lightbox)
- Add role="presentation" on overlay backdrops (NoteCard menu, emoji pickers)
- Add aria-label to all icon-only buttons (close, nav arrows, context menu)
- Add aria-expanded to context menu toggle
- Add meaningful alt text to all 35+ images (avatars, covers, thumbnails, media)
- Add aria-label to form inputs (search, onboarding login)

src/components/feed/InlineReplyBox.tsx

@@ -175,7 +175,7 @@ export function InlineReplyBox({ event, name, rootEvent }: InlineReplyBoxProps)
               ) : (
                 <img
                   src={url}
-                  alt=""
+                  alt="Attachment preview"
                   className="h-12 w-auto rounded-sm border border-border object-cover"
                   onError={(e) => { (e.target as HTMLImageElement).className = "h-12 w-16 rounded-sm border border-border bg-bg-raised"; }}
                 />