Add a Related tools section to tool pages

[anurag629]

Context

Part of the SEO growth initiative (#18): Phase 2: Coverage engine (guides and internal linking).
Today tool pages only link home. A "related tools / try next" section adds internal links that spread authority and keep visitors on-site.

What to do

• Add a small related-tools block to the shared tool page layout that surfaces 2-3 sibling tools from the registry.
• Use descriptive, keyword-rich anchor text (the tool name), not "click here".

Where

components/shared/ToolPageLayout.tsx, driven by lib/tools.ts.

Acceptance criteria

• Each tool page shows relevant sibling tools with descriptive anchors
• Light and dark themes unaffected
• 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.