fix: Newline renders as yoga carrier (text node) when standalone

Match Ink's behavior where Newline renders as ink-text (yoga carrier).
When inside a Text parent, Newline still renders as virtual-text for
inline behavior. When standalone, it renders as a text node so it
participates in yoga layout and occupies vertical space.

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

packages/runtime-tests/integration/components/newline-standalone.test.tsx

@@ -0,0 +1,42 @@
+import { defineComponent } from "vue";
+import { expect, test } from "vite-plus/test";
+import { render } from "@vue-tui/testing";
+import { Box, Text, Newline } from "@vue-tui/runtime";
+
+test("Newline works standalone (outside Text) as a yoga carrier", async () => {
+  // In Ink, Newline renders as ink-text (yoga carrier) so it works
+  // outside a Text context as a standalone line break.
+  const { lastFrame } = await render(
+    defineComponent(() => () => (
+      <Box flexDirection="column">
+        <Newline />
+        <Text>hi</Text>
+      </Box>
+    )),
+    { columns: 100 },
+  );
+  // Newline should occupy a line before "hi"
+  const frame = lastFrame({ trimLines: true })!;
+  const lines = frame.split("\n");
+  expect(lines.length).toBeGreaterThanOrEqual(2);
+  expect(lines.at(-1)).toBe("hi");
+});
+
+test("Newline count=2 adds two blank lines standalone", async () => {
+  const { lastFrame } = await render(
+    defineComponent(() => () => (
+      <Box flexDirection="column">
+        <Text>above</Text>
+        <Newline count={2} />
+        <Text>below</Text>
+      </Box>
+    )),
+    { columns: 100 },
+  );
+  const frame = lastFrame({ trimLines: true })!;
+  expect(frame).toContain("above");
+  expect(frame).toContain("below");
+  const lines = frame.split("\n");
+  // "above", 2 blank lines, "below" = at least 4 lines
+  expect(lines.length).toBeGreaterThanOrEqual(4);
+});