fix(config): open nano on the terminal in config edit

pkgmgr config edit ran nano through run_command, which pipes stdout and stderr to capture them, so nano aborted with 'Standard output is not a terminal'. The editor now runs with subprocess.call and the inherited terminal, and a failing editor exits with its code.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/unit/pkgmgr/cli/commands/test_config.py

@@ -0,0 +1,35 @@
+from __future__ import annotations
+
+import types
+import unittest
+from unittest.mock import patch
+
+from pkgmgr.cli.commands import config as config_cmd
+
+
+class ConfigEditTests(unittest.TestCase):
+    def _edit(self, path: str, returncode: int):
+        with patch(
+            "subprocess.Popen",
+            side_effect=AssertionError("the editor's output must not be captured"),
+        ), patch("subprocess.call", return_value=returncode) as call:
+            config_cmd.handle_config(
+                types.SimpleNamespace(subcommand="edit"),
+                types.SimpleNamespace(user_config_path=path),
+            )
+        return call
+
+    def test_nano_inherits_the_terminal(self):
+        call = self._edit("/cfg/config.yaml", 0)
+
+        call.assert_called_once_with(["nano", "/cfg/config.yaml"])
+
+    def test_a_failing_editor_exits_with_its_code(self):
+        with self.assertRaises(SystemExit) as raised:
+            self._edit("/cfg/config.yaml", 3)
+
+        self.assertEqual(raised.exception.code, 3)
+
+
+if __name__ == "__main__":
+    unittest.main()