Expose submission job status to users

[msaroufim]

Summary

• Include background job status on the authenticated user submission detail endpoint
• Preserve the existing submission response shape and add a nullable job object
• Add DB coverage for submissions with and without job status

Test

• uv run pytest tests/test_leaderboard_db.py tests/test_admin_api.py -q

[github-actions]

Coverage report

Click to see where and how coverage changed

File	Statements	Missing	Coverage	Coverage (new stmts)	Lines missing
src/libkernelbot
db_types.py
leaderboard_db.py
utils.py
Project Total

This report was generated by python-coverage-comment-action