update database schema for linking of persons and companies

src/wce_crm/db.py

@@ -7,7 +7,7 @@ from pathlib import Path
 
 import polars as pl
 import sqlalchemy as sql
-from sqlalchemy import Column, String, Table, TypeDecorator, event
+from sqlalchemy import Column, String, Table, TypeDecorator, UniqueConstraint, event
 
 from wce_crm import constants
 from wce_crm import types as t
@@ -420,6 +420,7 @@ zuordnung_personen_unternehmen: sql.Table = Table(
         UTCDateTime,
         nullable=True,
     ),
+    UniqueConstraint("un_id", "pers_id", name="uq_un_id_pers_id"),
 )