Add an isolated native WPF node editor and demo

[xincheng213618]

Summary

• Add a self-contained NativeWpf directory with a native WPF ST.Library.UI.WPF library, demo, documentation, and standalone solution.
• Keep the original DrawingTools.Graphics contract and present the GDI-rendered surface through a DPI-aware WPF WriteableBitmap.
• Keep the control library dependency-free; only WpfNodeEditorDemo references ColorVision.UI 1.5.7.
• Make the demo a full-window node canvas. Nodes are created from the integrated + button or the canvas context menu, so no TreeView or legacy property grid occupies permanent space.
• Generate a reflection-based property panel beside the single selected node. The demo adapter exposes only STNodePropertyAttribute properties and supplies native WPF editors for System.Drawing.Color, read-only values, and file selection.
• Include canvas and node context menus, automatic layout, save/open, undo/redo, clipboard actions, fit view, and an integrated execution command.
• Use cursor-centered wheel zoom in 0.05 steps across the 0.2-5.0 range, plus an explicit canvas drag lock whose manual state remains stable.

Isolation and compatibility

• Existing ST.Library.UI, WinNodeEditorDemo, legacy WpfNodeEdittorDemo, root README, and the original solution are unchanged by this PR.
• The new standalone solution only references projects inside NativeWpf.
• ST.Library.UI.WPF targets net8.0-windows and net10.0-windows and has no NuGet packages. The demo targets net8.0-windows/x64 because the published ColorVision assemblies are AMD64.
• The Demo's visual tree remains native WPF and contains no WindowsFormsHost. ColorVision.UI transitively brings ColorVision.Common, ColorVision.Themes, HandyControl, log4net, and Newtonsoft.Json; these dependencies do not enter the control library.
• Existing node namespaces, the original System.Drawing.Graphics drawing API, STND v1 behavior, and the historical WpfNodeEdittorDemo assembly identity are preserved.
• A consumer references either the WinForms implementation or the WPF implementation, not both assemblies in the same application.

Validation

• dotnet restore .\NativeWpf\STNodeEditor.Wpf.sln: successful.
• Debug and Release builds of both ST.Library.UI.WPF target frameworks: 0 warnings, 0 errors.
• Debug and Release builds of WpfNodeEditorDemo: 0 errors; a full rebuild retains the 66 nullable/member-hiding warnings from the copied sample nodes.
• dotnet list .\NativeWpf\ST.Library.UI.WPF\ST.Library.UI.WPF.csproj package --include-transitive: no packages for either target framework.
• Demo package audit: direct ColorVision.UI 1.5.7 only; its transitive dependencies are listed above.
• Startup smoke: the net8.0-windows demo is responsive with title STNodeEditor WPF Demo and closes normally with exit code 0.
• UI Automation: no Tree control; all AttrTestNode reflected properties are present; changing a string property survives closing and reopening the panel; changing the node title updates and repositions the panel; selecting all hides the single-node inspector.
• Zooming from 1.0 to 1.4 moves the node-anchored panel, and the integrated add menu still exposes the five sample node categories.
• Custom-editor STA smoke: the color and file editors both construct successfully with the packaged theme resources.
• Small-export regression check: a 1x1 canvas region at 0.5 scale returns a valid 1x1 image.
• Compatibility check: NumberInputNode retains assembly WpfNodeEdittorDemo and GUID f7bd9ac6-d33b-3fb6-87f8-6eb97692f71b.