Fix React error #31 crash from malformed Nostr profiles

Malformed profiles with non-string fields (e.g. nip05: {}) crashed
React's entire render tree in production. Add typeof guards and
profileName() utility across all components that render profile data.
Add ErrorBoundary in main.tsx to show crash details instead of blank screen.

src/components/feed/TextSegments.tsx

@@ -45,7 +45,8 @@ export function tryOpenNostrEntity(raw: string): boolean {
 export function MentionName({ pubkey, fallback }: { pubkey?: string; fallback: string }) {
   const profile = useProfile(pubkey ?? "");
   if (!pubkey) return <>{fallback}</>;
-  const name = profile?.displayName || profile?.name;
+  const raw = profile?.displayName || profile?.name;
+  const name = typeof raw === "string" ? raw : null;
   return <>{name || fallback}</>;
 }
 
@@ -65,7 +66,7 @@ export function renderTextSegments(
   segments.forEach((seg, i) => {
     switch (seg.type) {
       case "text":
-        elements.push(<span key={i}>{seg.value}</span>);
+        elements.push(<span key={i}>{typeof seg.value === "string" ? seg.value : String(seg.value)}</span>);
         break;
       case "link":
         elements.push(
@@ -79,7 +80,7 @@ export function renderTextSegments(
               if (tryHandleUrlInternally(seg.value)) e.preventDefault();
             }}
           >
-            {seg.display}
+            {typeof seg.display === "string" ? seg.display : String(seg.display)}
           </a>
         );
         break;
@@ -91,8 +92,8 @@ export function renderTextSegments(
             onClick={(e) => { e.stopPropagation(); tryOpenNostrEntity(seg.value); }}
           >
             @{resolveMentions
-              ? <MentionName pubkey={seg.mentionPubkey} fallback={seg.display ?? seg.value.slice(0, 12) + "…"} />
-              : seg.display}
+              ? <MentionName pubkey={seg.mentionPubkey} fallback={String(seg.display ?? seg.value).slice(0, 12) + "…"} />
+              : String(seg.display ?? seg.value)}
           </span>
         );
         break;
@@ -103,7 +104,7 @@ export function renderTextSegments(
             className="text-accent/80 cursor-pointer hover:text-accent"
             onClick={(e) => { e.stopPropagation(); openHashtag(seg.value); }}
           >
-            {seg.display}
+            {String(seg.display ?? seg.value)}
           </span>
         );
         break;