fix: keep navigation active on deep documentation pages

[PeterRamotowski]

Fixes

• replace the hand-maintained MkDocs nav block with a metadata-driven navigation hook
• include all principle, Core Skill, profile, modifier, language, framework, and evaluation detail pages in the actual navigation tree
• group the 72 principles by their canonical categories so the long catalogue stays structured and collapsible
• add explicit landing pages for Decision system, Technologies, Examples, and Reference
• fix the Reference top-level route so it resolves to /reference/ instead of a missing implicit section page
• keep the correct top tab and primary sidebar active on third-level pages

Verification

A temporary branch-only workflow (removed before this PR) successfully ran repository validation, normative linting, documentation generation, and mkdocs build. It also asserted against the generated HTML that:

• /reference/ is built
• Principles is the active top tab on Avoid Accidental Complexity
• the primary sidebar is present and contains that active principle
• Decision system is active on a reusable-library profile detail page

The distribution manifest was refreshed with the repository's existing manifest generator.