M8-R07: integrate WarmteLink device access into Compose

docker-compose.dev.yml

@@ -26,3 +26,7 @@ services:
       - "127.0.0.1:8002:8000"
     environment:
       APP_DATABASE_URL: "sqlite:////app/data/app.db"
+    devices: !override
+      - "${WARMTELINK_DEVICE_PATH:?Set a stable /dev/serial/by-id path}:/dev/warmtelink:rw"
+    group_add: !override
+      - "${WARMTELINK_SERIAL_GID:?Set the host serial device GID}"