feat: add useCursor composable for terminal cursor control

- setCursorPosition propagates to app context for frame restoration
- Cursor cleared on component unmount via onScopeDispose

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

packages/runtime-tests/integration/composables/use-cursor.test.tsx

@@ -0,0 +1,56 @@
+import { defineComponent, nextTick, shallowRef } from "vue";
+import { describe, expect, test } from "vite-plus/test";
+import { render } from "@vue-tui/testing";
+import { Text, useCursor } from "@vue-tui/runtime";
+
+describe("useCursor", () => {
+  test("setCursorPosition updates cursor state", async () => {
+    const App = defineComponent(() => {
+      const { setCursorPosition } = useCursor();
+      setCursorPosition({ x: 5, y: 3 });
+      return () => <Text>cursor test</Text>;
+    });
+    const { lastFrame } = await render(App);
+    expect(lastFrame()).toContain("cursor test");
+  });
+
+  test("setCursorPosition can be updated reactively", async () => {
+    const pos = shallowRef<{ x: number; y: number } | undefined>({ x: 0, y: 0 });
+    const App = defineComponent(() => {
+      const { setCursorPosition } = useCursor();
+      setCursorPosition(pos.value);
+      return () => <Text>reactive</Text>;
+    });
+    const { lastFrame } = await render(App);
+    expect(lastFrame()).toContain("reactive");
+
+    // Update position — should not crash
+    pos.value = { x: 10, y: 5 };
+    await nextTick();
+  });
+
+  test("setCursorPosition accepts undefined to hide cursor", async () => {
+    const App = defineComponent(() => {
+      const { setCursorPosition } = useCursor();
+      setCursorPosition({ x: 1, y: 1 });
+      setCursorPosition(undefined);
+      return () => <Text>hidden</Text>;
+    });
+    const { lastFrame } = await render(App);
+    expect(lastFrame()).toContain("hidden");
+  });
+
+  test("cursor is cleared on unmount", async () => {
+    const App = defineComponent(() => {
+      useCursor();
+      return () => <Text>cursor</Text>;
+    });
+    const { unmount } = await render(App);
+    unmount();
+    // No crash = success (cursor position cleared via onScopeDispose)
+  });
+
+  test("throws when called outside render tree", () => {
+    expect(() => useCursor()).toThrow("useCursor() must be called inside a vue-tui render tree");
+  });
+});

packages/runtime-tests/integration/public-api.test.ts

@@ -18,6 +18,7 @@ test("public API exposes documented members", () => {
     "useStdout",
     "useStderr",
     "useTerminalSize",
+    "useCursor",
   ]) {
     expect(api).toHaveProperty(k);
   }