refactor(#356): DSAR-Fachlogik vollstaendig aus dem Core extrahiert — dsar_collect/dsar_erase in die 5 beteiligten Contracts (contacts, mail, tasks, calendar, kommunikation); core/jobs.py sammelt/loescht nur Core-eigene Daten und iteriert generisch ueber die Plugin-Registry; neue Plugins liefern DSAR-Kategorien ohne Core-Aenderung; Counts-/Category-Keys unveraendert; tasks/contracts.py von Patch-Artefakt bereinigt

fixes #356

app/plugins/builtins/mail/contracts.py

@@ -16,6 +16,11 @@ instead of importing from internal modules directly.
 
 from __future__ import annotations
 
+from typing import Any
+
+from sqlalchemy import select
+from sqlalchemy.ext.asyncio import AsyncSession
+
 from app.plugins.builtins.contracts import get_contract_registry
 from app.plugins.builtins.mail.models import Mail, MailAccount
 
@@ -33,6 +38,32 @@ class MailContract:
     Mail = Mail
     MailAccount = MailAccount
 
+    @staticmethod
+    async def dsar_collect(
+        db: AsyncSession, tenant_id: Any, user_id: Any
+    ) -> dict[str, Any]:
+        """GDPR Art. 15: collect mail account data owned by the user."""
+        mail_accounts = (
+            await db.execute(
+                select(MailAccount).where(
+                    MailAccount.tenant_id == tenant_id,
+                    MailAccount.user_id == user_id,
+                ).limit(500)
+            )
+        ).scalars().all()
+        return {
+            "mail_accounts": [
+                {
+                    "id": str(a.id),
+                    "email_address": a.email_address,
+                    "display_name": a.display_name,
+                    "is_shared": a.is_shared,
+                    "is_active": a.is_active,
+                }
+                for a in mail_accounts
+            ]
+        }
+
     @classmethod
     def get_function(cls, name: str):
         """Return a callable exposed by this contract, or None if absent."""