feat(xcui): advance core and editor validation flow

tests/UI/Core/integration/README.md

@@ -1,8 +1,24 @@
-# Core UI Integration Notes
+# Core UI Integration Validation
 
-The core XCUI lane currently validates shared primitives through automated unit tests.
+This directory contains the manual XCUI validation system for shared Core primitives.
 
-Interactive validation belongs to:
+Structure:
 
-- `tests/UI/Runtime/integration/` for game/runtime UI
-- `tests/UI/Editor/integration/` for editor UI
+- `shared/`: shared host, native renderer, screenshot helper, scenario registry
+- `input/`: shared input validation category
+- `layout/`: shared layout validation category
+- `style/`: shared theme token and style resolution validation category
+- `text/`: shared UTF-8 text rendering and textInput focus marker validation category
+
+Rules:
+
+- One scenario directory maps to one executable.
+- Do not accumulate unrelated checks into one monolithic app.
+- Shared infrastructure belongs in `shared/`, not duplicated per scenario.
+- Screenshots are stored per scenario inside that scenario's `captures/` folder.
+
+Build:
+
+```bash
+cmake --build build --config Debug --target core_ui_integration_tests
+```