fix: use hex format for pubkey in NIP-11 document

The NIP-11 specification requires the pubkey field to be a 64-character
hex string, but we were incorrectly using npub (bech32) format.

Changes:
- Add Config::relay_owner_pubkey_hex() method to get hex format
- Update NIP-11 document to use hex format instead of npub
- Update test to verify 64-char hex string instead of npub format

Fixes nak relay command error:
'must be a hex string of 64 characters'

src/config.rs

@@ -574,7 +574,13 @@ impl Config {
         Keys::parse(nsec).context("Invalid relay_owner_nsec")
     }
 
-    /// Get the relay owner's public key (npub format) for NIP-11
+    /// Get the relay owner's public key (hex format) for NIP-11
+    pub fn relay_owner_pubkey_hex(&self) -> Result<String> {
+        let keys = self.relay_owner_keys()?;
+        Ok(keys.public_key().to_hex())
+    }
+
+    /// Get the relay owner's public key (npub format)
     pub fn relay_owner_npub(&self) -> Result<String> {
         let keys = self.relay_owner_keys()?;
         Ok(keys.public_key().to_bech32()?)

src/http/nip11.rs

@@ -100,7 +100,7 @@ impl RelayInformationDocument {
         Self {
             name: config.relay_name(),
             description: config.relay_description.clone(),
-            pubkey: config.relay_owner_npub().ok(),
+            pubkey: config.relay_owner_pubkey_hex().ok(),
             contact: None, // Could be added to config if needed
             supported_nips: vec![
                 1,  // NIP-01: Basic protocol flow
@@ -145,10 +145,11 @@ mod tests {
         assert_eq!(doc.name, "Test Relay");
         assert_eq!(doc.description, "A test relay");
 
-        // Verify pubkey is present and is a valid npub
+        // Verify pubkey is present and is a valid hex string (64 chars)
         assert!(doc.pubkey.is_some());
         let pubkey = doc.pubkey.unwrap();
-        assert!(pubkey.starts_with("npub1"));
+        assert_eq!(pubkey.len(), 64);
+        assert!(pubkey.chars().all(|c| c.is_ascii_hexdigit()));
 
         assert!(doc.supported_nips.contains(&1));
         assert!(doc.supported_nips.contains(&11));