Add CMake vcpkg UI validation target

docs/modernization/build-inventory.md

@@ -71,6 +71,7 @@ $env:VCPKG_ROOT = "C:\Program Files\Microsoft Visual Studio\2022\Community\VC\vc
 cmake --preset windows-msvc-vcpkg-headless
 powershell -ExecutionPolicy Bypass -File scripts\automation\platform-build.ps1 -Presets windows-msvc-vcpkg-headless
 ctest --preset desktop-fast-vcpkg --build-config Debug
+cmake --build --preset windows-msvc-default --config Debug --target panopainter_platform_build_vcpkg_ui_core
 cmake --preset android-arm64
 powershell -ExecutionPolicy Bypass -File scripts\automation\platform-build.ps1 -Presets android-arm64
 powershell -ExecutionPolicy Bypass -File scripts\automation\android-legacy-package-build.ps1 -Packages standard
@@ -99,6 +100,10 @@ Known local toolchain state:
 - Local Visual Studio generator selected by CMake: Visual Studio 17 2022
 - Bundled vcpkg: `C:\Program Files\Microsoft Visual Studio\2022\Community\VC\vcpkg`
   (`vcpkg version` reports 2025-11-19)
+- External vcpkg: `D:\vcpkg` is currently resolved by
+  `scripts/automation/platform-build.ps1` when `VCPKG_ROOT` is already set on
+  this host; the wrapper falls back to bundled Visual Studio vcpkg roots when
+  needed.
 - Android SDK: `C:\Users\omara\AppData\Local\Android\Sdk`
 - Android NDK: latest SDK Manager package selected by
   `scripts/automation/android-sdk-env.ps1`; currently
@@ -200,7 +205,8 @@ powershell -ExecutionPolicy Bypass -File scripts\automation\apple-remote-build.p
   root CMake package targets yet.
 - Root CMake exposes non-default platform validation targets:
   `panopainter_platform_build_headless`,
-  `panopainter_platform_build_android_assets`, and
+  `panopainter_platform_build_android_assets`,
+  `panopainter_platform_build_vcpkg_ui_core`, and
   `panopainter_platform_build_apple_remote`. These targets call the existing
   platform automation scripts from CMake and keep platform validation discoverable
   from the CMake target graph while app/package target migration remains open.
@@ -610,7 +616,9 @@ powershell -ExecutionPolicy Bypass -File scripts\automation\apple-remote-build.p
   of owning active WGL context/pixel-format attribute literals in `main.cpp`.
 - `windows-msvc-vcpkg-headless` validates manifest install/configure/build/test
   for the current headless component matrix; see DEBT-0007 for remaining app
-  and platform triplet migration.
+  and platform triplet migration. Root CMake target
+  `panopainter_platform_build_vcpkg_ui_core` focuses that gate on the
+  vcpkg-backed `pp_ui_core`/tinyxml2 boundary and `pp_ui_core_layout_xml_tests`.
 - `scripts/automation/analyze.*` runs shader validation plus a
   renderer-boundary guard that reports JSON and fails if active non-backend
   source code reintroduces raw `GL_*`/`WGL_*` constants outside the allowed