Add Creality K-series LAN discovery via DNS-SD mDNS

When a user adds a Creality K-series printer (host_type=crealityprint)
and clicks the existing "Browse" button in the Physical Printer dialog,
dispatch to a new CrealityDiscoveryDialog that finds K2 / K2 Plus /
K2 Pro printers on the LAN automatically. For other host types the
button keeps its existing BonjourDialog behaviour.

  CrealityHostDiscovery (src/slic3r/Utils/CrealityHostDiscovery.{hpp,cpp})

    Wraps the vendored cxmdns wrapper from the previous commit:

      static std::vector<CrealityHost> scan(bool probe_info = true);

    Calls cxnet::syncDiscoveryService({"Creality", "creality"}) to find
    K-series printers via DNS-SD, dedupes by IP, then optionally HTTP
    GETs http://<ip>/info on each match to fetch the model code
    (F008 = K2 Plus, F012 = K2 Pro, F021 = K2) and MAC. Returns enriched
    {ip, hostname, model_code, model_name, mac, cfs_capable} entries.

  CrealityDiscoveryDialog (src/slic3r/GUI/CrealityDiscoveryDialog.{hpp,cpp})

    Modal dialog with a wxListView showing Model / Hostname / IP per
    discovered host. Runs CrealityHostDiscovery::scan() synchronously
    with wxBusyCursor + wxWindowDisabler (5-10s total wait). User picks
    one, dialog returns the IP via selected_ip().

  PhysicalPrinterDialog (src/slic3r/GUI/PhysicalPrinterDialog.cpp)

    The "Browse" button's click handler now reads host_type from the
    edited config. If htCrealityPrint, opens CrealityDiscoveryDialog
    and writes "http://<ip>" into the print_host field. Otherwise the
    existing BonjourDialog path runs unchanged -- no behaviour change
    for OctoPrint / Moonraker / Klipper users.

No new UI surface: one existing button now does the right thing per
host_type, mirroring how Creality Print discovers its own printers.

src/slic3r/GUI/CrealityDiscoveryDialog.cpp

@@ -0,0 +1,122 @@
+#include "CrealityDiscoveryDialog.hpp"
+#include "slic3r/Utils/CrealityHostDiscovery.hpp"
+#include "GUI_App.hpp"
+#include "I18N.hpp"
+
+#include <wx/sizer.h>
+#include <wx/button.h>
+#include <wx/listctrl.h>
+#include <wx/stattext.h>
+#include <wx/utils.h>
+
+#include <boost/log/trivial.hpp>
+
+namespace Slic3r {
+namespace GUI {
+
+CrealityDiscoveryDialog::CrealityDiscoveryDialog(wxWindow* parent)
+    : wxDialog(parent, wxID_ANY, _L("Detect Creality K-series printer"),
+               wxDefaultPosition, wxDefaultSize, wxDEFAULT_DIALOG_STYLE | wxRESIZE_BORDER)
+{
+    const int em = wxGetApp().em_unit();
+
+    m_status = new wxStaticText(this, wxID_ANY, _L("Click Scan to look for K-series printers on your network."));
+
+    m_list = new wxListView(this, wxID_ANY, wxDefaultPosition, wxDefaultSize,
+                            wxLC_REPORT | wxSIMPLE_BORDER | wxLC_SINGLE_SEL);
+    m_list->SetMinSize(wxSize(50 * em, 18 * em));
+    m_list->AppendColumn(_L("Model"),    wxLIST_FORMAT_LEFT,  8 * em);
+    m_list->AppendColumn(_L("Hostname"), wxLIST_FORMAT_LEFT, 14 * em);
+    m_list->AppendColumn(_L("IP"),       wxLIST_FORMAT_LEFT, 14 * em);
+
+    auto* scan_btn   = new wxButton(this, wxID_ANY, _L("Scan"));
+    auto* ok_btn     = new wxButton(this, wxID_OK,     _L("Use Selected"));
+    auto* cancel_btn = new wxButton(this, wxID_CANCEL, _L("Cancel"));
+    ok_btn->Disable();
+
+    auto* button_sizer = new wxBoxSizer(wxHORIZONTAL);
+    button_sizer->Add(scan_btn,   0, wxALL, em);
+    button_sizer->AddStretchSpacer(1);
+    button_sizer->Add(ok_btn,     0, wxALL, em);
+    button_sizer->Add(cancel_btn, 0, wxALL, em);
+
+    auto* vsizer = new wxBoxSizer(wxVERTICAL);
+    vsizer->Add(m_status, 0, wxEXPAND | wxALL, em);
+    vsizer->Add(m_list,   1, wxEXPAND | wxALL, em);
+    vsizer->Add(button_sizer, 0, wxEXPAND);
+    SetSizerAndFit(vsizer);
+
+    scan_btn->Bind(wxEVT_BUTTON, [this](wxCommandEvent&) { run_discovery(); });
+
+    m_list->Bind(wxEVT_LIST_ITEM_SELECTED,   [ok_btn](wxListEvent&) { ok_btn->Enable(); });
+    m_list->Bind(wxEVT_LIST_ITEM_DESELECTED, [ok_btn](wxListEvent&) { ok_btn->Disable(); });
+    m_list->Bind(wxEVT_LIST_ITEM_ACTIVATED,  [this](wxListEvent&)   { on_ok(); EndModal(wxID_OK); });
+
+    ok_btn->Bind(wxEVT_BUTTON, [this](wxCommandEvent&) { on_ok(); EndModal(wxID_OK); });
+
+    wxGetApp().UpdateDlgDarkUI(this);
+
+    // Run discovery synchronously from the ctor so results are ready by the
+    // time the dialog is shown. Posting an async CallAfter from a ShowModal
+    // override risked the event firing after the modal loop had exited -- the
+    // captured `this` would then be a dangling stack pointer and subsequent
+    // UI access could fault.
+    run_discovery();
+}
+
+void CrealityDiscoveryDialog::run_discovery()
+{
+    m_status->SetLabel(_L("Scanning the LAN for K-series printers... this takes a few seconds."));
+    m_list->DeleteAllItems();
+    m_rows.clear();
+    Layout();
+    Update();
+
+    std::vector<CrealityHost> hosts;
+    {
+        wxBusyCursor cursor;
+        wxWindowDisabler disabler(this);
+        hosts = CrealityHostDiscovery::scan(/*probe_info=*/true);
+    }
+
+    for (const auto& h : hosts) {
+        Row row;
+        row.ip       = h.ip;
+        row.hostname = h.hostname;
+        if (!h.model_name.empty())
+            row.model = h.model_name;
+        else if (h.cfs_capable)
+            row.model = "(unknown K-series)";
+        else
+            row.model = "Creality";
+        m_rows.push_back(std::move(row));
+    }
+
+    for (size_t i = 0; i < m_rows.size(); ++i) {
+        long idx = m_list->InsertItem(i, wxString::FromUTF8(m_rows[i].model));
+        m_list->SetItem(idx, 1, wxString::FromUTF8(m_rows[i].hostname));
+        m_list->SetItem(idx, 2, wxString::FromUTF8(m_rows[i].ip));
+    }
+
+    if (m_rows.empty()) {
+        m_status->SetLabel(_L(
+            "No K-series printers found. Make sure the printer is on the same "
+            "network and not blocked by Wi-Fi client isolation, then click Scan again."));
+    } else {
+        m_status->SetLabel(wxString::Format(
+            _L("Found %zu Creality printer(s). Select one and click Use Selected."),
+            m_rows.size()));
+        m_list->Select(0);
+    }
+}
+
+void CrealityDiscoveryDialog::on_ok()
+{
+    auto sel = m_list->GetFirstSelected();
+    if (sel >= 0 && sel < int(m_rows.size())) {
+        m_selected_ip = m_rows[sel].ip;
+    }
+}
+
+} // namespace GUI
+} // namespace Slic3r