fix: pass APP_DOMAIN env to caddy, don't expose app port on host

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: baijum

deploy/docker-compose.standalone.yml

@@ -3,8 +3,8 @@ services:
     build:
       context: ..
       dockerfile: app/Dockerfile
-    ports:
-      - "8000:8000"
+    expose:
+      - "8000"
     env_file:
       - .env
     healthcheck:
@@ -38,6 +38,8 @@ services:
     ports:
       - "80:80"
       - "443:443"
+    env_file:
+      - .env
     volumes:
       - ./Caddyfile:/etc/caddy/Caddyfile
       - /data/todo-app/caddy:/data