fix: correct flex basis column test expectations to match Ink output

height=6 containers produce 6 lines. Ink's renderToString returns
"A\n\n\nB\n\n" (preserving trailing blank lines). The tests incorrectly
expected "A\n\n\nB" with a comment claiming lastFrame({ trimLines: true })
trims trailing newlines — it does not; it only trims trailing spaces per
line.

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

packages/runtime-tests/integration/layout/flex.test.tsx

@@ -115,8 +115,7 @@ test('set flex basis with flexDirection="column" container', async () => {
     )),
     { columns: 100 },
   );
-  // Ink: "A\n\n\nB\n\n" — trailing newlines trimmed by lastFrame({ trimLines: true })
-  expect(lastFrame({ trimLines: true })).toBe("A\n\n\nB");
+  expect(lastFrame({ trimLines: true })).toBe("A\n\n\nB\n\n");
 });
 
 test('set flex basis in percent with flexDirection="column" container', async () => {
@@ -131,6 +130,5 @@ test('set flex basis in percent with flexDirection="column" container', async ()
     )),
     { columns: 100 },
   );
-  // Ink: "A\n\n\nB\n\n" — trailing newlines trimmed by lastFrame({ trimLines: true })
-  expect(lastFrame({ trimLines: true })).toBe("A\n\n\nB");
+  expect(lastFrame({ trimLines: true })).toBe("A\n\n\nB\n\n");
 });