Expose FretDiagram setDot/setMarker/setBarre to plugin API

Add a FretDiagram wrapper class to the QML plugin API that exposes
the methods needed to programmatically set dots, markers (open/muted),
and barres on fretboard diagrams from plugins.

New Q_INVOKABLE methods:
- setDot(string, fret, add, dotType) — place a dot on a string/fret
- setMarker(string, markerType) — set open (O) or muted (X) marker
- setBarre(startString, endString, fret) — create a barre
- clear() — remove all dots/markers/barres

New Q_PROPERTY accessors:
- strings (read/write) — number of strings
- frets (read/write) — number of visible frets
- fretOffset (read/write) — starting fret position
- showNut (read/write) — toggle nut display

This follows the same wrapper pattern used by Note, Chord, Lyrics,
and other existing API wrapper classes. The wrapper delegates to the
existing FretDiagram dom class methods which already handle all the
internal logic.

Fixes #32798

Author: Dheeraj Chand

src/engraving/api/v1/elements.cpp

@@ -687,6 +687,7 @@ EngravingItem* mu::engraving::apiv1::wrap(mu::engraving::EngravingItem* e, Owner
     API_WRAP(DurationElement)
     API_WRAP(Beam)
     API_WRAP(Lyrics)
+    API_WRAP(FretDiagram)
     API_WRAP(Segment)
     API_WRAP(Measure)
     API_WRAP(MeasureBase)

src/engraving/api/v1/elements.h

@@ -27,6 +27,7 @@
 
 #include "engraving/dom/engravingitem.h"
 #include "engraving/dom/arpeggio.h"
+#include "engraving/dom/fret.h"
 #include "engraving/dom/barline.h"
 #include "engraving/dom/beam.h"
 #include "engraving/dom/bracketItem.h"
@@ -2665,6 +2666,76 @@ class Lyrics : public EngravingItem
     apiv1::EngravingItem* separator() const { return wrap(lyrics()->separator()); }
 };
 
+//---------------------------------------------------------
+//   FretDiagram
+/// Exposes FretDiagram dot, marker, and barre manipulation
+/// to the QML plugin API.
+/// \since MuseScore 4.7
+//---------------------------------------------------------
+
+class FretDiagram : public EngravingItem
+{
+    Q_OBJECT
+
+    /// Number of strings in the diagram.
+    Q_PROPERTY(int strings READ strings WRITE setStrings)
+    /// Number of frets shown in the diagram.
+    Q_PROPERTY(int frets READ frets WRITE setFrets)
+    /// Fret offset (0-based: value N means the top of the diagram is at fret N+1).
+    Q_PROPERTY(int fretOffset READ fretOffset WRITE setFretOffset)
+    /// Whether to show the nut (thick line at top of diagram).
+    Q_PROPERTY(bool showNut READ showNut WRITE setShowNut)
+
+public:
+    /// \cond MS_INTERNAL
+    FretDiagram(mu::engraving::FretDiagram* fd = nullptr, Ownership own = Ownership::PLUGIN)
+        : EngravingItem(fd, own) {}
+
+    mu::engraving::FretDiagram* fretDiagram() { return toFretDiagram(e); }
+    const mu::engraving::FretDiagram* fretDiagram() const { return toFretDiagram(e); }
+    /// \endcond
+
+    int strings() const { return fretDiagram()->strings(); }
+    void setStrings(int n) { fretDiagram()->setStrings(n); }
+    int frets() const { return fretDiagram()->frets(); }
+    void setFrets(int n) { fretDiagram()->setFrets(n); }
+    int fretOffset() const { return fretDiagram()->fretOffset(); }
+    void setFretOffset(int val) { fretDiagram()->setFretOffset(val); }
+    bool showNut() const { return fretDiagram()->showNut(); }
+    void setShowNut(bool val) { fretDiagram()->setShowNut(val); }
+
+    /// Set a dot on the specified string at the specified fret.
+    /// \param string 0-based string index (0 = highest pitched string)
+    /// \param fret fret number (1-based, 0 removes the dot)
+    /// \param add if true, add a second dot without removing existing ones
+    /// \param dotType dot type: 0=normal, 1=cross, 2=square, 3=triangle
+    Q_INVOKABLE void setDot(int string, int fret, bool add = false, int dotType = 0) {
+        fretDiagram()->setDot(string, fret, add,
+                              static_cast<mu::engraving::FretDotType>(dotType));
+    }
+
+    /// Set a marker on the specified string.
+    /// \param string 0-based string index (0 = highest pitched string)
+    /// \param markerType marker type: 0=none, 1=circle (open), 2=cross (muted)
+    Q_INVOKABLE void setMarker(int string, int markerType) {
+        fretDiagram()->setMarker(string,
+                                 static_cast<mu::engraving::FretMarkerType>(markerType));
+    }
+
+    /// Set a barre across strings at the specified fret.
+    /// \param startString 0-based start string index
+    /// \param endString 0-based end string index
+    /// \param fret fret number (1-based)
+    Q_INVOKABLE void setBarre(int startString, int endString, int fret) {
+        fretDiagram()->setBarre(startString, endString, fret);
+    }
+
+    /// Remove all dots, markers, and barres from the diagram.
+    Q_INVOKABLE void clear() {
+        fretDiagram()->clear();
+    }
+};
+
 #undef API_PROPERTY
 #undef API_PROPERTY_T
 #undef API_PROPERTY_READ_ONLY