fix: add default_peer_rpc_url for bulk sync fallback

- Add default_peer_rpc_url configuration parameter
- Update bulk sync fallback to use default_peer_rpc_url instead of gossip_broadcast_url
- Fixes 'unsupported protocol redis://' error in bulk sync
- gossip_broadcast_url is for Redis backend, not HTTP RPC calls

apps/blockchain-node/src/aitbc_chain/config.py

@@ -79,6 +79,7 @@ class ChainSettings(BaseSettings):
 
     gossip_backend: str = "memory"
     gossip_broadcast_url: Optional[str] = None
+    default_peer_rpc_url: Optional[str] = None  # HTTP RPC URL of default peer for bulk sync
 
     # NAT Traversal (STUN/TURN)
     stun_servers: str = ""  # Comma-separated STUN server addresses (e.g., "stun.l.google.com:19302,jitsi.example.com:3478")

apps/blockchain-node/src/aitbc_chain/main.py

@@ -158,8 +158,8 @@ class BlockchainNode:
                                     # Get source URL from block metadata if available
                                     source_url = block_data.get("source_url")
                                     if not source_url:
-                                        # Fallback to default peer URL from gossip backend
-                                        source_url = settings.gossip_broadcast_url
+                                        # Fallback to default peer RPC URL
+                                        source_url = settings.default_peer_rpc_url
                                     
                                     if source_url:
                                         try: