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/daemon/embedded_daemon.cpp

@@ -545,6 +545,15 @@ bool EmbeddedDaemon::start(const std::string& binary_path)
         args.push_back("-maxconnections=" + std::to_string(max_connections_));
     }
 
+    // Host a RandomX stratum pool from this node (-stratum). Only v1.3.0+ daemons implement it; older
+    // ones ignore the unknown flag (no fatal arg check), and the Settings toggle is gated on daemon
+    // version, so this is only enabled against a daemon that supports it. Without -stratumallowip the
+    // daemon serves loopback only (safe default); a subnet opens it to that LAN.
+    if (stratum_enabled_) {
+        args.push_back("-stratum");
+        if (!stratum_allowip_.empty()) args.push_back("-stratumallowip=" + stratum_allowip_);
+    }
+
     // Active wallet file (multi-wallet). The daemon loads <datadir>/<name>. Only pass it for a
     // non-default name so the common case's command line is unchanged; skip during an isolated
     // start (seed migration manages its own throwaway wallet).