Add check for user DID before key verification

Throws an error if the user DID is not available before attempting to verify the key on the server, preventing potential runtime errors.

src/lib/hooks/useSodiumChat.ts

@@ -61,6 +61,9 @@ export function useSodiumChat() {
 
           // Verify key exists on server
           console.log('[Sodium] Verifying key on server...');
+          if (!user.did) {
+            throw new Error('User DID not available');
+          }
           const checkResponse = await fetch(`/api/chat/keys?did=${encodeURIComponent(user.did)}`);
 
           let shouldPublish = false;