Consolidate behavioral tests and clarify documentation

[Kevin-Umali]

Summary

• Group scanner tests by behavior and remove self-referential rule/catalog checks.
• Exercise archive path and registry host edge cases through scanner output, with benign controls.
• Clarify trust and release evidence, improve documentation entry paths and navigation, and add an unreleased changelog entry.

Scanner runtime code and detection rules are unchanged. Site navigation and favicon are updated.

Validation

• make check
• Python script unit tests
• make format-check
• Astro format, type check, build, and documentation link checks
• Rendered documentation navigation review

Author and committer: Kevin Umali. No co-author trailer.