perf(nodes): Connected Nodes refresh — parallel probes, instant list, 12s health timeout

Reachability probes ran one at a time with a 30s Tor timeout each, so
Refresh sat disabled for N-offline-peers × 30s. Now the list renders and
the button re-enables immediately; probes run concurrently and fill the
dots in as they land.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

neode-ui/src/api/rpc-client.ts

@@ -447,7 +447,8 @@ class RPCClient {
     return this.call({
       method: 'node-check-peer',
       params: { onion },
-      timeout: 35000,
+      // Backend health-dial timeout is 12s — 15s here covers RPC overhead.
+      timeout: 15000,
     })
   }