pqcli: add --import-save and --export-save

--import-save FILE adds the character in a .pqw file to the roster;
it can be given more than once, and if any file fails, nothing is
imported. --export-save NUM FILE writes a character out. Export never
overwrites an existing file. The file handling lives in pqw.read_file
and pqw.write_file, so the interfaces can share it.

tests/test_cli.py

@@ -0,0 +1,57 @@
+import os
+import subprocess
+import sys
+from pathlib import Path
+
+from test_pqw import played
+
+from pqcli.game_data import load_game_data
+from pqcli.pqw import read_file, write_file
+
+
+def pqcli(
+    config: Path, *args: str, cwd: Path | None = None
+) -> subprocess.CompletedProcess[str]:
+    env = {**os.environ, "XDG_CONFIG_HOME": str(config)}
+    return subprocess.run(
+        [sys.executable, "-m", "pqcli", *args],
+        capture_output=True,
+        text=True,
+        env=env,
+        cwd=cwd,
+    )
+
+
+def test_import_then_export(tmp_path: Path) -> None:
+    data = load_game_data()
+    source = tmp_path / "in.pqw"
+    write_file(played(3000).player, source, data)
+
+    result = pqcli(tmp_path, "--import-save", str(source))
+    assert result.returncode == 0, result.stderr
+    assert result.stdout == "Imported Exportée\n"
+    assert (tmp_path / "pqcli" / "save.dat").exists()
+
+    listed = pqcli(tmp_path, "--list-saves")
+    assert listed.stdout == "1. Exportée\n"
+
+    target = tmp_path / "out.pqw"
+    result = pqcli(tmp_path, "--export-save", "1", str(target))
+    assert result.returncode == 0, result.stderr
+    assert read_file(target, data)[0].name == "Exportée"
+
+
+def test_import_bad_file_changes_nothing(tmp_path: Path) -> None:
+    bad = tmp_path / "bad.pqw"
+    bad.write_text("garbage!")
+    result = pqcli(tmp_path, "--import-save", str(bad))
+    assert result.returncode == 1
+    assert "not a .pqw file" in result.stderr
+    assert not (tmp_path / "pqcli" / "save.dat").exists()
+
+
+def test_export_rejects_unknown_character(tmp_path: Path) -> None:
+    result = pqcli(tmp_path, "--export-save", "3", str(tmp_path / "x.pqw"))
+    assert result.returncode == 1
+    assert "Invalid player" in result.stderr
+    assert not (tmp_path / "x.pqw").exists()