fix: resolve did:dht compilation errors

- Simplify DHT encoding: use JSON instead of DNS packets (drop simple-dns)
- Fix mainline crate API: SigningKey takes 32 bytes, get_mutable returns Result
- Add missing dht_did field to IdentityRecord constructor
- Store DID Document as JSON in DHT (DNS encoding deferred)

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

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

@@ -3,6 +3,38 @@ use anyhow::{Context, Result};
 use tracing::debug;
 
 impl RpcHandler {
+    /// server.set-name — Rename the server (persisted to data_dir/server-name)
+    pub(super) async fn handle_server_set_name(
+        &self,
+        params: Option<serde_json::Value>,
+    ) -> Result<serde_json::Value> {
+        let params = params.ok_or_else(|| anyhow::anyhow!("Missing params"))?;
+        let name = params
+            .get("name")
+            .and_then(|v| v.as_str())
+            .ok_or_else(|| anyhow::anyhow!("Missing required parameter: name"))?
+            .trim()
+            .to_string();
+
+        if name.is_empty() || name.len() > 64 {
+            anyhow::bail!("Name must be 1-64 characters");
+        }
+
+        // Persist to file
+        let name_file = self.config.data_dir.join("server-name");
+        tokio::fs::write(&name_file, &name)
+            .await
+            .context("Failed to write server name")?;
+
+        // Update live state
+        let (mut data, _) = self.state_manager.get_snapshot().await;
+        data.server_info.name = Some(name.clone());
+        self.state_manager.update_data(data).await;
+
+        debug!("Server name updated to: {}", name);
+        Ok(serde_json::json!({ "name": name }))
+    }
+
     /// system.stats — CPU usage, RAM used/total, disk used/total, uptime, load average
     pub(super) async fn handle_system_stats(&self) -> Result<serde_json::Value> {
         debug!("Getting system stats");