Add contextual internal links between guides and tools

[anurag629]

Context

Part of the SEO growth initiative (#18): Phase 2: Coverage engine (guides and internal linking).
Internal links are a ranking lever. Each guide should push readers to its tool, and each tool should point to its guide, forming a tight cluster.

What to do

• From each guide, link to the matching tool with a clear CTA.
• From each tool page, link to its guide where one exists.
• Use descriptive anchor text.

Where

Guides registry and components/shared/ToolPageLayout.tsx. Depends on the guides system.

Acceptance criteria

• Guides link to tools and tools link to their guides
• npm run lint && npm run test && npm run build passes

Notes

Branch off develop (feat/*, docs/*, chore/*), open a PR into develop, and squash-merge. See CONTRIBUTING.md.
Depends on the guides content system.