Fix CLI stdout count report + add regression test

Devin Review caught that `--out -` discarded the sample count, so
the stderr summary always said 'wrote 0 sample(s)' even when bytes
were streamed. Capture the return value like the file-output branch
does, and add a regression test that exercises the stdout path.

Co-Authored-By: adrian kuman firmansah <adriancuman@gmail.com>

src/ocr_sprint/tools/export_ground_truth.py

@@ -101,9 +101,8 @@ def main(argv: list[str] | None = None) -> int:
     )
 
     out: Path = args.out
-    count = 0
     if str(out) == "-":
-        _write_stream(sys.stdout.buffer, filters)
+        count = _write_stream(sys.stdout.buffer, filters)
     else:
         out.parent.mkdir(parents=True, exist_ok=True)
         with out.open("wb") as fh:

tests/unit/test_cli_export_ground_truth.py

@@ -65,6 +65,22 @@ def test_cli_respects_limit(db_ready: None, tmp_path: Path) -> None:
     assert len(lines) == 1
 
 
+def test_cli_stdout_reports_correct_count(
+    db_ready: None, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """``--out -`` writes JSONL to stdout; the "wrote N" message must
+    reflect what actually streamed, not 0."""
+    _seed_two_approved_jobs()
+    exit_code = export_main(["--out", "-"])
+    assert exit_code == 0
+    captured = capsys.readouterr()
+    stdout_lines = [line for line in captured.out.splitlines() if line.strip()]
+    assert len(stdout_lines) == 2
+    for line in stdout_lines:
+        assert json.loads(line)["approved"] is True
+    assert "wrote 2 sample(s)" in captured.err
+
+
 def test_cli_print_stats_emits_json_to_stderr(
     db_ready: None, tmp_path: Path, capsys: pytest.CaptureFixture[str]
 ) -> None: