v0.1.0

First release. The code was developed inside com.gdk.core on the feat/uitk-migration
branch and extracted here — not unchanged: every file referenced the host framework,
and severing those references is most of what this release is. See "Changed on extraction"
below for what that cost.

Added

• A standalone UI Toolkit screen layer. Screens are UXML documents parented into a
  UIDocument's visual tree. BaseUIToolkitView, UIToolkitViewFactory,
  VisualElementViewLayer.
• Its own contracts, in Runtime/Core/: IUIToolkitView (the view lifecycle),
  IViewLayer / IViewSurface (where a view lives and how it moves),
  IVisualTreeAssetLoader (one method — the host supplies the asset pipeline), and
  IPresenterInstantiator (the collection adapters' presenter factory).
• RootUIDocument plus the default three-layer RootUIDocument.uxml, and a Layers
  value carrying the Screen / Hidden / Overlay layers as one thing.
• Collection adapters — list, grid and multi-template — with IUIToolkitItemView,
  BaseUIToolkitItemView and BaseUIToolkitItemPresenter.
• SafeAreaElement / SafeAreaCalculator — notch handling. Insets are applied as
  layout, either as padding or as absolute edges. Note that
  PanelSettings.SetScreenToPanelSpaceFunction is deliberately NOT used: it is present in
  6000.3.9f1, but it transforms pointer coordinates, so driving a safe area through it
  would move where clicks land without moving any layout.
• PanelScaleRatio — the CanvasScaler-equivalent aspect-ratio rule, applied to
  PanelSettings. It clones the settings asset by default, because PanelSettings is a
  shared project asset and writing to it at runtime is a source-control diff rather than a
  runtime tweak.
• BackNavigationSource — raises a C# event on NavigationCancelEvent, covering
  Escape, gamepad B and the Android back button.
• A VContainer registration, in its own assembly. See Dependencies below — it began
  as an optional, gated assembly and is not one any more.
• A Notification Popup sample and 113 PlayMode tests.

Dependencies

• VContainer is required, not optional. jp.hadashikick.vcontainer is a real dependency
  and the registration assembly is no longer gated behind a GDK_VCONTAINER versionDefine
  plus a matching defineConstraints. The project standardises on VContainer for all
  dependency injection, so a host without a container is not a supported configuration — and
  the gate was an assembly-level branch that nothing exercised. Cuvara.UIToolkit.VContainer
  stays a separate assembly for direction rather than for gating: it may reference the view
  and manager types, and they may not reference it, which is what keeps a container reference
  out of the view layer.
• com.cysharp.unitask and com.unity.modules.uielements are the other two. All three
  resolve from a registry, so the package installs from its own declarations — the OpenUPM
  scoped registry for com.cysharp and jp.hadashikick is the consuming project's to add,
  because a UPM package cannot declare a scoped registry of its own.

Changed on extraction

Every one of these was a reference to com.gdk.core that had to be severed, not a
refactor for its own sake:

• ISurfaceScreenView / IScreenViewBase → IUIToolkitView. The host contract required a
  RectTransform and an IsReadyToUse flag; a VisualElement has no Transform, and
  CloneTree is synchronous so there is no "not ready yet" window to flag.
• IViewLayer / IViewSurface are now DEFINED here. The host deleted its copies and
  consumes these, so there is one definition rather than two.
• IAssetsManager → IVisualTreeAssetLoader. The host's loader comes from an OpenUPM
  scoped registry, and a UPM package cannot declare a scoped registry of its own — so that
  dependency could never have resolved for a consumer installing from a git URL.
• The collection adapters' IDependencyContainer, resolved through a static service
  locator, → IPresenterInstantiator passed in. That locator was both a dependency and the
  reason those adapters could not be exercised without a live scene.
• SignalBus → plain C# events. ILoggerManager → UnityEngine.Debug.
• Namespaces GameFoundation.Scripts.UIModule.UITK.* → Cuvara.UIToolkit.*; assemblies
  GameFoundation.UIModule.UITK → Cuvara.UIToolkit.

Deliberately not here

UIToolkitScreenViewBackend, BaseUIToolkitScreenPresenter,
BaseUIToolkitPopupPresenter, the notification popup presenter, and the back-navigation
policy all stayed in com.gdk.core. Each one exists to bind this package to that
framework — it implements IScreenViewBackend, or takes a SignalBus, or decides what
Back closes. Moving them here would have re-created the dependency this package exists to
remove. A CI gate (.github/scripts/check_standalone.py) fails the build if any of those
host symbols reappears under Runtime/ or Tests/.