Normalize plugin lifecycle failures

[biru-codeastromer]

Summary

• normalize entry-point discovery, loading, identity, and interface failures to SS060
• require non-empty declared plugin names and versions, with the declared name matching the requested entry point
• preserve official-loader SS060 failures while normalizing custom-loader, interface-property, analysis-iteration, and evidence failures to SS061
• add adversarial regressions and document the stable error boundary

Validation

• make release-gate: 103 passed, 1 optional skip, 92.79% coverage
• missing, wrong-type, empty, mismatched, and throwing identity/version cases covered
• arbitrary SplitSealError values from custom loading, generator iteration, and version access normalize to SS061 without their original details
• combined exact-head #23/Normalize excessive structured input nesting #31/Normalize plugin lifecycle failures #34 gate: 147 passed, 1 optional skip, 92.98% coverage, clean 0.4.0 install, Parquet, signatures, audits, example, and Gitleaks
• combined streaming benchmark peak: 719,685 Python bytes at 10,000 records and 709,659 at 50,000 records
• package, dependency, example, text, repository, and secret audits passed

This PR is intentionally left unmerged pending maintainer review.

[biru-codeastromer]

Superseded by merged #41, which preserves this change in the protected v0.4.0 release stack.