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.h

@@ -182,6 +182,7 @@ public:
      * @brief Set maximum peer connections (0 = use daemon default)
      */
     void setMaxConnections(int v) { max_connections_ = v; }
+    void setStratumHosting(bool enabled, const std::string& allowIp) { stratum_enabled_ = enabled; stratum_allowip_ = allowIp; }
 
     /**
      * @brief Request a blockchain rescan on the next daemon start
@@ -311,6 +312,8 @@ private:
     std::atomic<bool> should_stop_{false};
     std::set<std::string> debug_categories_;
     int max_connections_ = 0;  // 0 = daemon default
+    bool stratum_enabled_ = false;   // -stratum: host a RandomX pool (v1.3.0+; older daemons ignore it)
+    std::string stratum_allowip_;    // -stratumallowip subnet (empty = daemon default: loopback only)
     std::string wallet_file_;  // -wallet=<name> for the active wallet; empty/"wallet.dat" = default
     std::atomic<int> crash_count_{0};  // consecutive crash counter
     std::atomic<bool> rescan_on_next_start_{false};  // -rescan flag for next start