docs(readme): correct status and add topology

[JasonTM17]

Summary

• replace the stale Dependabot count with a live filtered queue
• frame DevHire as a Java, systems, and DevOps learning project
• add a clearly labeled simplified service topology with detailed architecture link

Verification

• README links resolve to tracked documentation
• topology matches the documented service groups
• git diff --check passes

Scope

Documentation only; no runtime, deployment, or dependency changes.

[JasonTM17]

Superseded by #113, which consolidated every pending branch, resolved compatibility and security conflicts, passed the complete protected CI/Docker/Trivy matrix, and was squash-merged as 1af5202. This branch is now redundant.