Fix Laravel APP_KEY handling in Docker

Export the generated Laravel app key before starting Apache so deployments without an explicit APP_KEY do not fail with a 500 MissingAppKeyException.

docker-compose.yml

@@ -11,7 +11,7 @@ services:
       APP_URL: ${APP_URL:-http://localhost}
       APP_ENV: ${APP_ENV:-production}
       APP_DEBUG: ${APP_DEBUG:-false}
-      APP_KEY: ${APP_KEY:-}
+      APP_KEY: ${APP_KEY}
       DB_HOST: ${DB_HOST:-db}
       DB_PORT: ${DB_PORT:-3306}
       DB_USER: ${DB_USER:-spota_user}