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/main.tsx

@@ -1,15 +1,42 @@
 import "./lib/tauri-dev-mock"; // must be first — mocks Tauri invoke() in browser dev mode
-import { StrictMode } from "react";
+import { StrictMode, Component, type ReactNode } from "react";
 import { createRoot } from "react-dom/client";
 import App from "./App";
 import "./index.css";
 import { useUserStore } from "./stores/user";
 
+// Error boundary to catch React error #31 and show details instead of blank screen
+class ErrorBoundary extends Component<{ children: ReactNode }, { error: Error | null }> {
+  state: { error: Error | null } = { error: null };
+  static getDerivedStateFromError(error: Error) { return { error }; }
+  componentDidCatch(error: Error, info: React.ErrorInfo) {
+    console.error("[Vega] React error boundary caught:", error, info.componentStack);
+  }
+  render() {
+    if (this.state.error) {
+      return (
+        <div style={{ padding: 20, color: "#ff6b6b", fontFamily: "monospace", fontSize: 13 }}>
+          <h2>Vega crashed</h2>
+          <pre style={{ whiteSpace: "pre-wrap", wordBreak: "break-all" }}>
+            {this.state.error.message}
+          </pre>
+          <pre style={{ whiteSpace: "pre-wrap", wordBreak: "break-all", color: "#aaa", marginTop: 10 }}>
+            {this.state.error.stack}
+          </pre>
+        </div>
+      );
+    }
+    return this.props.children;
+  }
+}
+
 // Restore session — pubkey (read-only) or nsec via OS keychain
 useUserStore.getState().restoreSession();
 
 createRoot(document.getElementById("root") as HTMLElement).render(
   <StrictMode>
-    <App />
+    <ErrorBoundary>
+      <App />
+    </ErrorBoundary>
   </StrictMode>,
 );