fix: update JwtService to handle default expiration and add tests for token generation

docker-compose.prod.yml

@@ -9,7 +9,7 @@ services:
       SPRING_DATASOURCE_PASSWORD: ${SPRING_DATASOURCE_PASSWORD}
       APP_PASSWORD: ${APP_PASSWORD}
       JWT_SECRET: ${JWT_SECRET}
-      JWT_EXPIRATION_MS: ${JWT_EXPIRATION_MS}
+      JWT_EXPIRATION_MS: ${JWT_EXPIRATION_MS:-86400000}
       MAIL_HOST: ${MAIL_HOST}
       MAIL_PORT: ${MAIL_PORT}
       MAIL_USERNAME: ${MAIL_USERNAME}