feat(frontend): add instance badge to remote author posts in feed

thoughts-frontend/components/thought-card.tsx

@@ -165,9 +165,14 @@ export function ThoughtCard({
                 {author.displayName || author.username}
               </span>
               {!author.local && (
-                <span className="text-xs text-muted-foreground/70 truncate">
-                  {author.username.startsWith("@") ? author.username : `@${author.username}`}
-                </span>
+                <div className="flex items-center gap-1.5 min-w-0">
+                  <span className="text-xs text-muted-foreground/70 truncate">
+                    {author.username.startsWith("@") ? author.username : `@${author.username}`}
+                  </span>
+                  <span className="text-[10px] font-medium px-2 py-0.5 rounded-full bg-blue-500/10 border border-blue-500/20 text-blue-500 shrink-0">
+                    {author.username.split("@").filter(Boolean).at(-1)}
+                  </span>
+                </div>
               )}
               <time
                 dateTime={new Date(thought.createdAt).toISOString()}