[codex] Align git workflow and deployments

[jjoonleo]

Summary

• Run PR tests for both dev and main, and let failed tests block merge instead of auto-closing PRs.
• Move production deployment from the retired deploy branch to main with manual dispatch support and the production environment.
• Add a separate dev deployment workflow using DEV_ secrets, development environment, and isolated dev server/container settings.
• Document the new branch workflow and update deployment docs for the dev/prod server model.

Validation

• Parsed all GitHub workflow YAML files successfully.
• Ran git diff --check before commit.