feat(network): give the "no peers" banner an honest detail and a Restart action

The no-peers banner headline ("Connected, but no network peers") was followed
by a detail line that just repeated connection_status ("Connected"/"Peers: 0"),
reading as a contradiction, and it offered no action at the exact moment the
wallet looks synced but is silently stalled at a stale height.

- NoPeers now clears the passthrough detail; App renders a translated,
  actionable hint (node_banner_no_peers_detail) for this reason instead.
- When the embedded daemon is the node, offer a Restart button (re-triggers
  peer discovery via the -addnode seeds); an external node stays action-less
  since it is the user's own to restart.
- Update + extend the evaluator unit tests (external = no action/empty detail;
  embedded = RestartNode).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/util/i18n.cpp

@@ -1543,6 +1543,7 @@ void I18n::loadBuiltinEnglish()
         // Persistent node-status banner (App::renderNodeStatusBanner).
         strings_["node_banner_offline_title"] = "Not connected to the DragonX node";
         strings_["node_banner_no_peers_title"] = "Connected, but no network peers — the node can't sync";
+        strings_["node_banner_no_peers_detail"] = "Check your internet connection and firewall, then restart the node to find peers.";
         strings_["node_banner_crashed_title"] = "The node stopped unexpectedly";
         strings_["node_banner_lite_open_failed"] = "Couldn't open your wallet";
         strings_["node_banner_reconnect"] = "Reconnect";