Task 22: Continuous test coverage note

Updated README.md near the top with a static coverage note linking to the CI workflow:
**Coverage**: ~71% combined (core + deployment) - see [CI coverage job](.github/workflows/ci.yml) for the latest.

Verification:
`grep -n "coverage\|Coverage" README.md | head -5`

Output:
12:**Coverage**: ~71% combined (core + deployment) - see [CI coverage job](.github/workflows/ci.yml) for the latest.
