[Change] docs-13: Fix navigation, add search, theme toggle & role-based navigation

[djm81]

OpenSpec Change: docs-13-nav-search-theme-roles

Why

docs-06 through docs-12 created per-bundle command pages, overview pages, workflow consolidation, and team/enterprise docs, but the sidebar navigation was never updated to link to them. Three bundles (Code Review, Spec, Govern) still point to generic /reference/commands/, Codebase is missing command pages, Team & Enterprise links to stale paths, and Workflows omits four new guides. The homepage has the same stale links. Beyond navigation fixes, the site lacks light/dark mode, search, and role-based navigation.

What Changes

• Fix all broken sidebar and homepage links across all bundles and sections
• Extract navigation into _data/nav.yml to prevent future drift
• Add light/dark mode toggle with SpecFact brand colors, localStorage persistence, theme-aware Mermaid
• Add Lunr.js client-side search with front matter metadata index, keyboard shortcuts
• Add expertise-level filter (beginner/intermediate/advanced) and role-based homepage entry cards
• Enrich front matter with keywords, audience, expertise_level on all pages
• Refine theme — cleaner sidebar, better code blocks, breadcrumbs, both light/dark modes

Capabilities

New: docs-nav-data-driven, docs-theme-toggle, docs-client-search, docs-role-expertise-nav
Modified: bundle-overview-pages, cross-module-workflow-docs, team-setup-docs, modules-docs-command-validation

Artifacts

• Proposal
• Design
• Specs (8 spec files, 25 requirements, 59 scenarios)
• Tasks (34 tasks in 7 groups)

Dependencies

Depends on: docs-06 through docs-12 (all implemented)