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/api/rpc/node.rs

@@ -71,7 +71,7 @@ impl RpcHandler {
     }
 
     pub(super) async fn handle_node_tor_address(&self) -> Result<serde_json::Value> {
-        let tor_address = docker_packages::read_tor_address("archipelago");
+        let tor_address = docker_packages::read_tor_address("archipelago").await;
         Ok(serde_json::json!({ "tor_address": tor_address }))
     }