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/article/ArticleView.tsx

@@ -43,7 +43,7 @@ function AuthorRow({ pubkey, publishedAt, readingTime }: { pubkey: string; publi
     <div className="flex items-center gap-3 mb-6">
       <button className="shrink-0" onClick={() => openProfile(pubkey)}>
         {profile?.picture ? (
-          <img src={profile.picture} alt="" className="w-9 h-9 rounded-sm object-cover hover:opacity-80 transition-opacity"
+          <img src={profile.picture} alt={`${name}'s avatar`} className="w-9 h-9 rounded-sm object-cover hover:opacity-80 transition-opacity"
             onError={(e) => { (e.target as HTMLImageElement).style.display = "none"; }} />
         ) : (
           <div className="w-9 h-9 rounded-sm bg-bg-raised border border-border flex items-center justify-center text-text-dim text-sm">
@@ -361,7 +361,7 @@ export function ArticleView() {
                 <div className="mb-6 -mx-2">
                   <img
                     src={image}
-                    alt=""
+                    alt={`Cover image for ${title || "article"}`}
                     className="w-full aspect-video object-cover rounded-sm"
                     onError={(e) => { (e.target as HTMLImageElement).style.display = "none"; }}
                   />