fix(input): allow Enter key to work when allowMultilinePaste is enabled

The bug was in `TextInput`: with `allowMultilinePaste` enabled, a
standalone Enter key could match the newline-paste fallback before
submit handling.

Change:

- Only treat newline input as paste fallback when `input.length > 1`.
- Added regression test: multiline value + `allowMultilinePaste` + Enter
  submits and does not call `onChange`.

Author: remarkablemark

src/components/TextInput/TextInput.test.tsx

@@ -136,6 +136,25 @@ describe('TextInput', () => {
     expect(onSubmit).toHaveBeenCalledWith('test');
   });
 
+  it('submits on Enter when multiline paste is enabled', async () => {
+    const onChange = vi.fn();
+    const onSubmit = vi.fn();
+    const { stdin } = render(
+      <TextInput
+        value={'one\ntwo'}
+        allowMultilinePaste
+        onChange={onChange}
+        onSubmit={onSubmit}
+      />,
+    );
+
+    stdin.write(KEY.ENTER);
+    await time.tick();
+
+    expect(onSubmit).toHaveBeenCalledWith('one\ntwo');
+    expect(onChange).not.toHaveBeenCalled();
+  });
+
   it('inserts bracketed pasted text with newlines without submitting', async () => {
     const onChange = vi.fn();
     const onSubmit = vi.fn();

src/components/TextInput/TextInput.tsx

@@ -150,7 +150,8 @@ export function TextInput({
         return;
       }
 
-      const hasPastedNewlines = allowMultilinePaste && /[\r\n]/.test(input);
+      const hasPastedNewlines =
+        allowMultilinePaste && input.length > 1 && /[\r\n]/.test(input);
 
       if (hasPastedNewlines) {
         insertText(normalizePastedText(input));