build: stabilize quality gates for 0.5.1

[cloudQuant]

Summary

• repairs the local MyPy hook and excludes test-temporary files from packaging checks
• adds static root-API contracts and source/wheel API checks to CI and publish verification
• updates 0.5.1 release metadata, docs, provenance, and reproducible quality baseline

Evidence

• 1,921 passed, 14 skipped locally; non-integration quality baseline: 1,841 passed, 15 skipped, 76.0% branch coverage
• package build, Twine, release consistency, release-candidate, notices, and static source/wheel API checks passed
• no fincore/ runtime module changes

Scope

This is a quality-only 0.5.1 release. Legacy core source-complexity cleanup remains explicitly deferred pending the missing project coding-rule source and behavior baselines.