Add optional QML-based map view (QQuickWidget) with feature flag and migration notes

[axelvonkamp]

Motivation

• Introduce an experimental Qt Quick / QML based map canvas to enable a hardware-accelerated rendering path while preserving the existing QGraphicsView implementation as the default.
• Provide a smooth migration path so the rest of the codebase can treat either backend as a drop-in map widget.

Description

• Add a new QmlMapView implementation in cnapy/gui_elements/qml_map_view.py which exposes a QmlMapController and ReactionBoxListModel to QML and mirrors the MapView API and signals.
• Add QML UI files qml/MapView.qml and qml/ReactionBoxDelegate.qml that render the map background, reaction boxes, panning/zooming, selection, context menu and drag/drop behavior.
• Introduce factory/helper functions create_cnapy_map_view and is_cnapy_map_view in central_widget.py, use them where MapView was constructed or type-checked, and keep existing MapView behavior as the default; enable QML path when CNAPY_QML_MAP_VIEW=1.
• Update main_window.py to import and use the factory and type helper, and add migration documentation docs/qml-map-view-migration.md describing architecture and porting notes.

Testing

• Ran the project's automated test suite with pytest which completed successfully.
• Performed an automated syntax/compile check with python -m compileall . which succeeded.

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Codex Task