feat: Mini-Apps registry, Stammdaten backend persistence, bank accounts

- Register 6 mini-apps in kommunikation plugin (contact_picker, file_share,
  calendar_invite, mail_forward, ai_search, task_create)
- Connect AdressenTab to backend API (GET/POST/PATCH/DELETE /addresses)
- Create BankAccount model, schema, service, routes + migration 0033
- Connect KontenTab to backend API (GET/POST/PATCH/DELETE /bank-accounts)
- AI tools already working: 7 tools registered (hybrid_search, get_contact_mails, etc.)

app/models/__init__.py

@@ -1,6 +1,7 @@
 """SQLAlchemy models for LeoCRM."""
 
 from app.models.address import Address
+from app.models.bank_account import BankAccount
 from app.models.ai_conversation import AIConversation, AIMessage
 from app.models.attachment import Attachment
 from app.models.audit import AuditLog, DeletionLog
@@ -48,6 +49,7 @@ __all__ = [
     "SystemSettings",
     "Attachment",
     "Address",
+    "BankAccount",
     "Plugin",
     "PluginMigration",
     "AIConversation",