feat(mail): define standard IMAP folder mappings

tests/test_mail_config.py

@@ -2,10 +2,39 @@ from __future__ import annotations
 
 import unittest
 
-from govoplan_core.mail.config import normalize_split_transport_credentials
+from govoplan_core.mail.config import ImapServerConfig, normalize_split_transport_credentials
 
 
 class MailConfigTests(unittest.TestCase):
+    def test_legacy_sent_folder_populates_standard_mapping(self) -> None:
+        config = ImapServerConfig.model_validate(
+            {"host": "imap.example.test", "sent_folder": " Sent Items "}
+        )
+
+        self.assertEqual("Sent Items", config.sent_folder)
+        self.assertIsNotNone(config.folder_mappings)
+        assert config.folder_mappings is not None
+        self.assertEqual("Sent Items", config.folder_mappings.sent)
+
+    def test_standard_sent_mapping_remains_legacy_append_default(self) -> None:
+        config = ImapServerConfig.model_validate(
+            {
+                "host": "imap.example.test",
+                "sent_folder": "Old Sent",
+                "folder_mappings": {
+                    "inbox": " INBOX ",
+                    "sent": "Sent Items",
+                    "junk": " ",
+                },
+            }
+        )
+
+        self.assertEqual("Sent Items", config.sent_folder)
+        assert config.folder_mappings is not None
+        self.assertEqual("INBOX", config.folder_mappings.inbox)
+        self.assertEqual("Sent Items", config.folder_mappings.sent)
+        self.assertIsNone(config.folder_mappings.junk)
+
     def test_normalize_split_transport_credentials_moves_legacy_auth_fields(self) -> None:
         payload = normalize_split_transport_credentials(
             {