Add persistence for the database

.gitignore

@@ -4,3 +4,4 @@
 python-venv/
 tickmate-backup-20230524.db
 server/public/
+db.mount/

docker-compose.yml

@@ -24,6 +24,8 @@ services:
       POSTGRES_DB: kalkulog
     secrets: [ postgres-password ]
     networks: [ internal ]
+    volumes:
+      - ./db.mount:/var/lib/postgresql/data
 
 secrets:
   postgres-password: