feat(gui): per-filament nozzle volume selection and persistence

- FilamentMapDialog's manual page understands volume types: a mixed
  (Hybrid) extruder shows separate Standard / High Flow drop zones
  with live sub-nozzle counts, a validation timer with an inline
  error + "set nozzle count" suggestion, and composes a per-filament
  volume map on OK (persisted to the plate or globally)
- switching an extruder's Flow type rewrites the affected plate map
  entries; plate maps stay sized across filament add/delete/count
  changes (values keep their filament, no index shift)
- CLI: manual mapping on multi-nozzle printers synthesizes the volume
  map from extruder flow types when absent; nozzle-manual mode
  requires explicit maps; computed maps land on the plate so exported
  projects carry filament_volume_maps
- filament_nozzle_map joins the project options (selection seeding +
  filament-count resizing)
- pot entries for the new dialog strings

All 19 reference fixtures byte-identical; slicing an exported Hybrid
project reproduces its g-code byte-for-byte with the volume map
round-tripped through model_settings.config.

src/slic3r/GUI/DragDropPanel.hpp

@@ -3,6 +3,7 @@
 
 #include "GUI.hpp"
 #include "GUI_Utils.hpp"
+#include "Widgets/Label.hpp"
 
 #include <wx/simplebook.h>
 #include <wx/dialog.h>
@@ -13,17 +14,20 @@
 
 namespace Slic3r { namespace GUI {
 
+wxDECLARE_EVENT(wxEVT_DRAG_DROP_COMPLETED, wxCommandEvent);
+
 wxColor Hex2Color(const std::string& str);
 
 class ColorPanel;
 class DragDropPanel : public wxPanel
 {
 public:
-    DragDropPanel(wxWindow *parent, const wxString &label, bool is_auto);
+    DragDropPanel(wxWindow *parent, const wxString &label, bool is_auto, bool has_title = true, bool is_sub = false);
 
     void AddColorBlock(const wxColour &color, const std::string &type, int filament_id, bool update_ui = true);
     void RemoveColorBlock(ColorPanel *panel, bool update_ui = true);
     void DoDragDrop(ColorPanel *panel, const wxColour &color, const std::string &type, int filament_id);
+    void UpdateLabel(const wxString &label);
 
     std::vector<int> GetAllFilaments() const;
 
@@ -35,9 +39,12 @@ public:
 private:
     wxBoxSizer *m_sizer;
     wxGridSizer *m_grid_item_sizer;
+    Label       *m_title_label = nullptr;
     bool         m_is_auto;
 
     std::vector<ColorPanel *> m_filament_blocks;
+
+    void NotifyDragDropCompleted();
 private:
     bool m_is_draging = false;
 };
@@ -64,6 +71,49 @@ private:
     int            m_filament_id;
 
 };
+
+// Drop zone for one extruder that can split into two sub-zones (High Flow / Standard)
+// when the extruder mixes nozzle volume types (Hybrid flow), and collapses back to a
+// single unified zone otherwise.
+class SeparatedDragDropPanel : public wxPanel
+{
+public:
+    SeparatedDragDropPanel(wxWindow *parent, const wxString &label, bool use_separation = false);
+
+    void AddColorBlock(const wxColour &color, const std::string &type, int filament_id, bool is_high_flow = false, bool update_ui = true);
+    void RemoveColorBlock(ColorPanel *panel, bool update_ui = true);
+
+    std::vector<int> GetAllFilaments() const;
+    std::vector<int> GetHighFlowFilaments() const;
+    std::vector<int> GetStandardFilaments() const;
+    std::vector<int> GetTPUHighFlowFilaments() const;
+
+    std::vector<ColorPanel *> get_filament_blocks() const;
+    std::vector<ColorPanel *> get_high_flow_blocks() const;
+    std::vector<ColorPanel *> get_standard_blocks() const;
+
+    void SetUseSeparation(bool use_separation);
+    bool IsUseSeparation() const { return m_use_separation; }
+    void ClearAllBlocks();
+    void UpdateLabel(const wxString &label);
+
+private:
+    void UpdateLayout();
+
+    wxBoxSizer   *m_main_sizer;
+    wxPanel      *m_content_panel;
+    wxBoxSizer   *m_content_sizer;
+    wxPanel      *m_separator = nullptr;
+    Label        *m_label;
+
+    DragDropPanel *m_high_flow_panel;
+    DragDropPanel *m_standard_panel;
+
+    DragDropPanel *m_unified_panel;
+
+    bool m_use_separation;
+};
+
 }} // namespace Slic3r::GUI
 
 #endif /* slic3r_DragDropPanel_hpp_ */