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.h

@@ -400,6 +400,11 @@ public:
     // Daemon — maximum peer connections (0 = daemon default)
     int getMaxConnections() const { return max_connections_; }
     void setMaxConnections(int v) { max_connections_ = std::max(0, v); }
+    // Host a RandomX stratum pool from the node (v1.3.0+ daemons). Empty allow-IP = loopback only (safe).
+    bool getStratumHost() const { return stratum_host_enabled_; }
+    void setStratumHost(bool v) { stratum_host_enabled_ = v; }
+    const std::string& getStratumAllowIp() const { return stratum_allowip_; }
+    void setStratumAllowIp(const std::string& v) { stratum_allowip_ = v; }
 
     // Lite wallet server selection
     LiteServerSelectionPreferenceMode getLiteServerSelectionMode() const { return lite_server_selection_mode_; }
@@ -617,6 +622,8 @@ private:
     bool keep_daemon_running_ = false;
     bool stop_external_daemon_ = false;
     int  max_connections_ = 0;  // 0 = daemon default
+    bool stratum_host_enabled_ = false;   // host a RandomX stratum pool from the node (v1.3.0+ daemons)
+    std::string stratum_allowip_;         // -stratumallowip filter (empty = daemon default: loopback only)
 
     // Lite wallet server preferences. These are user/server settings only;
     // wallet secrets, wallet files, and lifecycle state are never stored here.