Callback-based zoom/offset workaround for Avalonia PanAndZoom

[Copilot]

Avalonia's PanAndZoom ZoomBorder only exposes zoom and offset as read-only (unlike WPF's two-way bindable ZoomPanel), and the absolute offset values are unreliable. This makes the existing ViewTabViewModel binding-driven approach non-functional for Avalonia.

Approach

Adds a readOnlyZoomAndOffsets constructor parameter to ViewTabViewModel (default false, WPF untouched). When true, programmatic view changes (Fill, Fit, Zoom100, scrolling) use registered callbacks that directly manipulate ZoomBorder.SetMatrix() instead of pushing values through bindings.

Changes

• ViewTabViewModel — new bool readOnlyZoomAndOffsets ctor param; ApplyTransformCallback(zoom, tx, ty) for absolute transforms; PanStepCallback(dx, dy) for incremental panning. All mutating methods (Fill, Fit, Zoom100, DefferedFill, StartScrollingAsync) branch on the flag.
• MainWindow.Methods.axaml.cs — RegisterZoomBorderCallbacks() wires callbacks to ZoomBorder.SetMatrix() via Dispatcher.UIThread.Post
• MainWindow.axaml.cs — registers callbacks on Opened for both source/target panels
• MainWindow.axaml — removed PanelAttributesAP.* and OffsetX/OffsetY bindings from both ZoomBorders (replaced by callbacks); retained ZoomX/ZoomY OneWayToSource so the VM still reads gesture zoom
• App.DI.axaml.cs — passes readOnlyZoomAndOffsets: true for both ViewTabViewModel registrations

WPF project: zero files changed.

// Avalonia view registration
viewTab.ApplyTransformCallback = (zoom, tx, ty) =>
{
    Dispatcher.UIThread.Post(() =>
    {
        panel.SetMatrix(Matrix.CreateScale(zoom, zoom) *
                        Matrix.CreateTranslation(tx, ty));
    });
};

viewTab.PanStepCallback = (dx, dy) =>
{
    Dispatcher.UIThread.Post(() =>
    {
        panel.SetMatrix(panel.Matrix * Matrix.CreateTranslation(dx, dy));
    });
};

Scrolling in read-only mode uses a 1-second step interval per the issue requirements rather than the WPF 3ms continuous loop.