[codex] Add dev remote PC deploy workflow

[jjoonleo]

Summary

• add a development deploy workflow for the remote Ubuntu/Linux PC
• add a Docker Compose dev overlay that runs private MySQL alongside the backend
• add a Spring dev profile and update deployment/git workflow docs

Impact

• pushes to dev can deploy the backend to the remote PC using the development environment
• production deploy remains unchanged in .github/workflows/deploy.yml
• dev MySQL is managed by Compose and is not exposed publicly by default

Validation

• docker compose -f docker-compose.yml -f docker-compose.dev.yml config
• parsed GitHub workflow YAML with Ruby YAML loader
• cd ontime-back && ./gradlew test currently fails on the origin/dev base with existing Flyway/H2 application-context failures unrelated to these deploy-only changes