Migrate from v2

1. Update the host to Dear ImGui docking commit 367b2c24f399988ddafc0bb4628da0106bcc09be, including matching official backends and Test Engine sources.
2. Include <imkit/preview_opengl3.h> for GLFunctions and OpenGL3Renderer. <imkit/preview.h> now contains renderer-neutral types only. On macOS link imkit::preview_metal and pass borrowed MTLDevice/command buffers.
3. Replace Win32ActionSink with NativeActionSink. The callback returns bool and receives an optional UTF-8 value. Link the matching accessibility_win32 or accessibility_macos target.
4. Remove IMKIT_BUILD_WINDOW_FRAME_LEGACY_IMGUI and legacy target references. All consumers use the normal v3 targets and the exact pinned Dear ImGui ABI.
5. Installed consumers set IMKIT_SDK_ABI_CONFIRMED=ON only after matching the recorded OS, architecture, compiler, ImGui revision and imconfig ABI.
6. Link imkit::node_editor explicitly when adopting the new Node Editor. Move graph data, revision checks, edit application, Undo, evaluation and persistence into the host; do not treat the companion Material Graph model as library state.

Moving on to 4.0

The spellings deprecated after 3.3, the changed default tokens and the other changes that can affect hosts are listed in the 4.0 migration guide.