fix: resolve CodiMD startup warnings

- Fix health check endpoint from /healthz to / (root path)
- Add CMD_DOMAIN environment variable to resolve domain warning
- Add CMD_URL_ADDPORT and CMD_PROTOCOL_USESSL configuration
- Update .env.example with domain configuration examples

Co-Authored-By: Claude Sonnet 4 <noreply@anthropic.com>

docker-compose.yml

@@ -33,6 +33,9 @@ services:
     container_name: codimd-app
     environment:
       - CMD_DB_URL=${CMD_DB_URL}
+      - CMD_DOMAIN=${CMD_DOMAIN}
+      - CMD_URL_ADDPORT=${CMD_URL_ADDPORT}
+      - CMD_PROTOCOL_USESSL=${CMD_PROTOCOL_USESSL}
       - CMD_USECDN=false
       - CMD_SESSION_SECRET=${CMD_SESSION_SECRET}
       - CMD_SESSION_LIFETIME=1209600000
@@ -46,7 +49,7 @@ services:
       - ./upload-data:/home/hackmd/app/public/uploads
     restart: always
     healthcheck:
-      test: ["CMD", "wget", "--spider", "-q", "http://localhost:3000/healthz"]
+      test: ["CMD", "wget", "--spider", "-q", "http://localhost:3000/"]
       interval: 30s
       timeout: 10s
       retries: 3