v0.28.0: feat: native reproduction JUnit with protected report outputs

Releases PR #132 individually as quantfit 0.28.0.

• quantfit/reproduce_junit.py:reproduction_to_junit and reproduce --junit PATH render ten stable cases from the existing native decision. Unknown T0 skips, negative T0 fails, and only the native reproduced / 0 / passed=true result passes overall; void or unverified outcomes cannot produce an all-green suite.
• Loose-report and portable-bundle input modes preserve JSON and exit semantics. Bounded operational-error XML carries no fabricated comparison or raw provider/path diagnostics.
• JSON/XML are staged together and replaced atomically per file, with successful XML last. Consumed sources, both destinations and aliases are protected; publication faults exit 2 without claiming a transaction across the pair.
• Existing installed consumers and cold-report hooks exercise XML with historical aggregates and labeled synthetic controls. No additional model run, hosted job or dependency is introduced.

Released independently from PR #132: reproduction JUnit.

The introduced implementation passed exact-head hosted source acceptance; publication separately qualifies the exact versioned distributions.

Native decisions and JUnit do not establish
independent execution, authenticated labels, sensitivity, safety or scientific GO.

Exact-head validation passed before the protected merge. Publishing requalifies and attests the exact merged wheel and sdist; public artifact and provenance verification is tracked separately.