refactor: replace blocking std::fs and TCP I/O with async tokio equivalents

- R6: Convert 6 std::fs calls in session.rs to tokio::fs async
- R7: Convert std::fs::read_to_string in docker_packages.rs to async
- R8: Convert 3 std::fs calls in port_allocator.rs to async, switch to tokio::sync::Mutex
- R9+R10+R11: Fix blocking I/O in node_message.rs and nostr_discovery.rs
- R12: Convert electrs_status.rs from sync TCP to async tokio::net with 5s timeouts
- R4+R5: Spawn periodic cleanup tasks for endpoint and login rate limiters

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

core/archipelago/src/node_message.rs

@@ -56,13 +56,19 @@ pub async fn init(data_dir: &Path) {
 }
 
 /// Persist current messages to disk.
+/// Serializes under the lock, then writes asynchronously via spawn_blocking
+/// to avoid blocking the tokio runtime.
 fn persist() {
     let guard = store().lock().unwrap_or_else(|e| e.into_inner());
     let path_guard = data_path().lock().unwrap_or_else(|e| e.into_inner());
     if let Some(ref path) = *path_guard {
         if let Ok(content) = serde_json::to_string(&*guard) {
-            // Use sync write — called from store functions already holding the lock
-            let _ = std::fs::write(path, content);
+            let path = path.clone();
+            drop(path_guard);
+            drop(guard);
+            tokio::task::spawn(async move {
+                let _ = tokio::fs::write(&path, content).await;
+            });
         }
     }
 }