[CI] Integrate Automated Test Coverage & XML Reporting

[aviralsaxena16]

Resolves #30

Following the establishment of the backend CI pipeline #21 and the deterministic fixture framework #22 , this PR introduces the final foundational testing component: Visibility.

It adds visibility into code coverage metrics to identify testing blind spots and guide systematic reliability improvements.

Enhancements

• Automated Terminal Reporting: Injected pytest-cov into the CI matrix. The pipeline now automatically prints a --cov-report=term-missing table directly in the GitHub Actions logs.
• Actionable Metrics: Reviewers can now instantly see the exact percentage of app/ code covered by our regression tests, and specifically which line numbers remain untested (as seen in the attached screenshot).
• Future-Proofing (XML Output): Configured the workflow to generate a coverage.xml report. This requires zero overhead right now but perfectly sets the stage for a 1-click integration with Codecov or Coveralls in the future.

Why No Hard Threshold Yet?

To avoid unnecessarily failing the build for other contributors, I have intentionally omitted a hard --cov-fail-under flag. This allows us to establish our current baseline coverage naturally. Once we are comfortable with the baseline, we can enforce a soft threshold (e.g., 70%) to prevent coverage from degrading as we scale toward DCE/DSC modalities.

This PR builds upon the regression framework introduced in #22.

Local Coverage Run: