chore: add env_file: stack.env to all compose services

Portainer git-stack deployments require an explicit env_file reference
in the compose file to load variables from the repo's stack.env.
Adds env_file: [stack.env] before every service-level environment:
block across all 10 stacks.

stacks/monitoring/docker-compose.yml

@@ -19,6 +19,8 @@ services:
     image: ghcr.io/homarr-labs/homarr:latest
     restart: unless-stopped
     networks: [edge]
+    env_file:
+      - stack.env
     environment:
       - SECRET_ENCRYPTION_KEY=${HOMARR_SECRET_ENCRYPTION_KEY}
     ports: