feat(mining): host a RandomX stratum pool from the node (v1.3.0+)

Add an opt-in "Host a mining pool (stratum)" toggle so a v1.3.0+ node can run its native
RandomX stratum server for other miners to point at. Settings toggle + optional allow-IP/CIDR;
passes -stratum (+ -stratumallowip) to the daemon launch args, mirroring the -maxconnections
plumbing (EmbeddedDaemon::setStratumHosting <- DaemonController::syncSettings <- Settings).

Backwards compatible / safe by default:
- UI gated on daemon_version >= 1030000, so it's never offered where it would do nothing.
- The launch flag is harmless on older daemons (they ignore unknown args), and the toggle can
  only be enabled while connected to a v1.3.0+ node anyway.
- Blank allow-IP => the daemon serves loopback only (its safe default); entering a subnet opens
  it to that LAN, with an explicit exposure warning in the UI.
- Takes effect on the next daemon start/restart.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/config/settings.cpp

@@ -252,6 +252,8 @@ bool Settings::load(const std::string& path)
         loadScalar(j, "keep_daemon_running", keep_daemon_running_);
         loadScalar(j, "stop_external_daemon", stop_external_daemon_);
         loadScalar(j, "max_connections", max_connections_);
+        loadScalar(j, "stratum_host_enabled", stratum_host_enabled_);
+        loadScalar(j, "stratum_allowip", stratum_allowip_);
         if (j.contains("lite_wallet") && j["lite_wallet"].is_object()) {
             const auto& lite = j["lite_wallet"];
             if (lite.contains("server_selection_mode")) {
@@ -525,6 +527,8 @@ bool Settings::save(const std::string& path)
     j["keep_daemon_running"] = keep_daemon_running_;
     j["stop_external_daemon"] = stop_external_daemon_;
     j["max_connections"] = max_connections_;
+    j["stratum_host_enabled"] = stratum_host_enabled_;
+    j["stratum_allowip"] = stratum_allowip_;
     {
         json lite = json::object();
         lite["server_selection_mode"] = liteServerSelectionPreferenceModeName(lite_server_selection_mode_);