fix(#356): DSAR-Sammlung auf Contract-Zugriff umgestellt — 4 Core→Plugin-Imports (mail/tasks/calendar/kommunikation) nutzen jetzt get_contract(); MailContract exponiert MailAccount; ImportError-Fallback-Semantik unverändert; Checker 4→0 Verstöße; DSAR-Suite 4/4 passed

fixes #356

app/plugins/builtins/mail/contracts.py

@@ -17,20 +17,21 @@ instead of importing from internal modules directly.
 from __future__ import annotations
 
 from app.plugins.builtins.contracts import get_contract_registry
-from app.plugins.builtins.mail.models import Mail
+from app.plugins.builtins.mail.models import Mail, MailAccount
 
 
 class MailContract:
     """Public API surface for the mail plugin.
 
-    Exposes the ``Mail`` ORM model so that other plugins can query the
-    mails table without importing from ``mail.models`` directly.
+    Exposes ORM models so that other plugins can query the mail tables
+    without importing from ``mail.models`` directly.
     """
 
     contract_name = "mail"
 
     # ─── models ───
     Mail = Mail
+    MailAccount = MailAccount
 
     @classmethod
     def get_function(cls, name: str):