Fix npub encoding and validation errors

- Fixed frontend to properly encode npub using nip19.npubEncode()
- Enhanced backend to handle both npub and hex pubkey formats
- Resolved 'Data must be at least 6 characters long' validation error
- Added proper error handling for pubkey format validation
- Should eliminate retry loop issues during authentication

app.js

@@ -225,7 +225,20 @@ app.post('/complete-auth/:sessionId', async (req, res) => {
       throw new Error('Challenge mismatch');
     }
     
-    const { data: pubkey } = nip19.decode(npub);
+    // Handle both npub format and raw hex pubkey
+    let pubkey;
+    try {
+      if (npub.startsWith('npub')) {
+        const decoded = nip19.decode(npub);
+        pubkey = decoded.data;
+      } else {
+        // Assume it's raw hex pubkey
+        pubkey = npub;
+      }
+    } catch (error) {
+      throw new Error('Invalid public key format');
+    }
+    
     if (event.pubkey !== pubkey) {
       throw new Error('Public key mismatch');
     }