fix: expand configured service usernames

tests/test_config.py

@@ -2,6 +2,7 @@ import os
 import tempfile
 import unittest
 from pathlib import Path
+from unittest.mock import patch
 
 from archive_clients.config import ClientConfig, ConfigError, RootMapping
 
@@ -18,10 +19,15 @@ class ConfigTests(unittest.TestCase):
             (root / "sync").mkdir()
             config_path = root / "client.toml"
             config_path.write_text(
-                _config(root, role="cache"), encoding="utf-8"
+                _config(root, role="cache").replace(
+                    'username = "admin"', 'username = "${QB_USER}"'
+                ),
+                encoding="utf-8",
             )
-            config = ClientConfig.load(config_path, "archive")
+            with patch.dict(os.environ, {"QB_USER": "admin"}):
+                config = ClientConfig.load(config_path, "archive")
             self.assertEqual(config.role, "archive")
+            self.assertEqual(config.qbittorrent.username, "admin")
             self.assertEqual(config.read_shared_token(), "token")
             self.assertEqual(
                 config.qbittorrent.roots.api_to_local("/downloads/a/b"),