feat(docs): add documentation site

[lodev09]

Summary

Adds a documentation site in docs/ built with Next.js 16 and Fumadocs, to be deployed on Vercel at https://maps.lodev09.com.

• Landing page with hero, code sample beside a themed vector map illustration, features grid, and component cards
• Existing component docs moved from docs/*.md to docs/content/docs/**/*.mdx with frontmatter; new Introduction, Installation, and Usage pages
• Built-in search, sidebar, and table of contents
• SEO: sitemap, robots, canonical URLs, generated Open Graph images per page, and JSON-LD structured data
• README now points to the site; AGENTS.md and CONTRIBUTING.md reference the new docs location
• docs added as a yarn workspace with yarn docs dev; root lint, typecheck, jest, and prettier exclude it

Vercel: set the project Root Directory to docs.

Type of Change

• Bug fix
• New feature
• Breaking change
• Documentation update

Test Plan

• yarn docs dev: all routes, search API, sitemap, robots, and OG image routes return 200
• Verified landing page and docs pages in light and dark mode
• yarn docs typecheck, root yarn typecheck, and root yarn lint pass

Screenshots / Videos

N/A

Checklist

• I tested on iOS
• I tested on Android
• I tested on Web
• I updated the documentation (if needed)