Sentry Integration: Dynamic release tagging #1242

Describe the current behavior
Sentry reports a static release (0.5.0) for both kaapi-production and kaapi-staging, with no commits or deploys attached. Neither environment can show which commit or deploy introduced an issue.

Describe the enhancement you'd like
Tag every deploy with kaapi-backend@<tag or main>+<git sha 12> and register it in Sentry with its commits. Production and staging deploy through different workflows, so the CI/CD changes are split into two sub-issues:

• Sentry release tracking for production (git sha + deploy markers) #1240 Production: tag push → ECS (create-release.yml)
• Sentry Integration: Track staging commits #1241 Staging: main merge → EC2 (deploy-staging.yml)

The release-id code change (resolve_sentry_release, RELEASE_TAG setting, Dockerfile build arg) is shared; land it with whichever sub-issue goes first.

Why is this enhancement needed?
Regression detection, suspect commits and "resolved in next release" in Sentry all depend on a release id that changes per deploy.

Additional context
Draft implementation and runbook: #1234.