feat: fix DWN sync to use federation peers and standard port

- DWN sync now uses federation node list instead of old peer list
- Fix sync URL to use port 80 (nginx) instead of 5678 (direct backend)
- DWN /dwn endpoint now accessible without auth for peer sync
- Support both message formats: {message:{}} and {messages:[{}]}
- Replace request["message"] with unified message variable

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

core/archipelago/src/network/dwn_sync.rs

@@ -156,7 +156,7 @@ async fn sync_single_peer(
     local_messages: &[crate::network::dwn_store::DwnMessage],
     last_sync: &Option<String>,
 ) -> Result<u64> {
-    let base_url = format!("http://{}:5678", onion);
+    let base_url = format!("http://{}", onion);
     let mut imported = 0u64;
 
     // Step 1: Check peer health