docs: align the cron, teammate-pane and TUI comments with the paste

- cron resolvePrompt(): give the reason the rest of the cron docs give (the
  submit check cannot recognise a multi-line paste; in paste mode the newlines
  reach the CLI as keys) instead of the old one about writeViaMux fusing lines.
- sendInputToPane(): it types with send-keys -l and strips line breaks, so it
  no longer uses "the same approach as sendInput()".
- TUI client: newlines become spaces (the docstring said stripped), and the
  test name no longer cites "multi-line breaks Ink".

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

test/tui/tui-client.test.ts

@@ -327,7 +327,7 @@ describe('TuiClient.sendInput', () => {
     expect(JSON.parse(recorded[0].body)).toMatchObject({ input: 'hello world\r', useMux: true });
   });
 
-  it('collapses embedded newlines into spaces (multi-line breaks Ink)', async () => {
+  it('collapses embedded newlines into spaces (a multi-line paste cannot be confirmed as submitted)', async () => {
     await client().sendInput('abc', 'echo A\necho B\r\nline three  ');
     expect(JSON.parse(recorded[0].body).input).toBe('echo A echo B line three\r');
   });