Show test coverage in core package README via Codecov badge

[bedus-creation]

Summary

Adds a live Codecov coverage badge to the core package README and wires CI to publish coverage.

Changes

• Create fastapi_startkit/README.md (did not exist previously) with a live Codecov badge, plus PyPI/Python-version badges, an overview, install/extras, features, and development instructions.
• Update .github/workflows/test.yml:
  • Collect coverage on the fastapi_startkit test run: pytest tests/ -v --cov --cov-report=xml.
  • Add a codecov/codecov-action@v5 step uploading fastapi_startkit/coverage.xml for slug fastapi-startkit/fastapi-startkit-modules (flag fastapi_startkit).

Coverage is already configured in fastapi_startkit/pyproject.toml (pytest-cov, [tool.coverage.*], source = src/fastapi_startkit), so no config changes were needed there.

Notes

• The Codecov upload uses secrets.CODECOV_TOKEN; the badge renders live once the repo is set up on Codecov and coverage is uploaded from a CI run.
• fail_ci_if_error: false keeps the test job green even if the upload has a transient failure.

[bedus-creation]

REVIEW VERDICT: APPROVE (posted as comment — GitHub blocks self-approval).

Docs + CI only, no code/ORM/SQL changes.

Verified:

• --cov-report=xml writes coverage.xml into the fastapi_startkit working-directory; Codecov step's files: fastapi_startkit/coverage.xml (repo-root relative) resolves correctly.
• README Codecov badge slug matches codecov-action slug (fastapi-startkit/fastapi-startkit-modules).
• codecov-action@v5, token via secret, fail_ci_if_error: false.
• README dev install command matches the CI install line exactly.

Note (non-blocking): enabling --cov activates the fail_under = 50 gate in pyproject, so the CI test job now fails if total coverage drops below 50%. Assumed intentional.