feat: DID persistence + federation node names in sync

Part 1 — DID Persistence:
- Deploy script creates /var/lib/archipelago/identity/ directory
- First-boot script creates identity dir with proper ownership
- Identity load now logs pubkey to confirm persistence across restarts

Part 2 — Node Names:
- NodeStateSnapshot includes node_name field
- build_local_state() passes server name to sync responses
- update_node_state() stores peer's announced name on the FederatedNode
- Names propagate automatically during federation.sync-state

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

core/archipelago/src/api/rpc/federation.rs

@@ -328,8 +328,9 @@ impl RpcHandler {
 
         let tor_active = data.server_info.tor_address.is_some();
 
+        let server_name = data.server_info.name.clone().filter(|n| !n.is_empty());
         let state = federation::build_local_state(
-            apps, 0.0, 0, 0, 0, 0, 0, tor_active,
+            apps, 0.0, 0, 0, 0, 0, 0, tor_active, server_name,
         );
 
         Ok(serde_json::to_value(&state)?)