Build XCUI splitter foundation and test harness

tests/UI/Editor/integration/input/pointer_states/View.xcui

@@ -0,0 +1,30 @@
+<View
+  name="EditorInputPointerStates"
+  theme="../../shared/themes/editor_validation.xctheme">
+  <Column padding="24" gap="16">
+    <Card
+      title="Editor Validation | Pointer States"
+      subtitle="当前批次：鼠标 hover / focus / active / capture"
+      tone="accent"
+      height="90">
+      <Column gap="8">
+        <Text text="这是 editor 侧验证场景，不承载 runtime 游戏 UI。" />
+        <Text text="这一轮只检查鼠标输入状态，不混入别的控件实验。" />
+      </Column>
+    </Card>
+
+    <Card title="Pointer Input" subtitle="hover focus active capture" height="196">
+      <Column gap="12">
+        <Text text="这一轮只需要检查下面这三个按钮。" />
+        <Row gap="12">
+          <Button id="input-hover" text="Hover / Focus" />
+          <Button id="input-capture" text="Pointer Capture" capturePointer="true" />
+          <Button id="input-route" text="Route Target" />
+        </Row>
+        <Text text="1. 鼠标移到左侧按钮：hover 应变化，focus 保持空。" />
+        <Text text="2. 按住中间按钮：focus、active、capture 都应留在中间。" />
+        <Text text="3. 拖到右侧再松开：hover 移到右侧，capture 清空，focus 仍留中间。" />
+      </Column>
+    </Card>
+  </Column>
+</View>