Refactor site structure; add docs and search

Large refactor to reorganize the documentation site: rewrote README with new project structure and usage, updated .gitignore, and removed legacy markdown/config files. Added a Next.js app layout with dedicated home and docs routes (including error/loading pages and a dynamic docs [...slug] page), an API search route backed by fumadocs-core, and several UI components (plugin cards, provider, custom image, search). Introduced new lib helpers (config, layout.shared, mdx-link, source, utils), MDX components, fetch-docs script, PostCSS/next config updates, and TypeScript config tweaks. Removed optional server-only API routes and other deprecated files to streamline static GitHub Pages deployment and improve doc fetching, search, and site UX.

Author: cklei-carly

.gitignore

@@ -5,6 +5,7 @@
 .contentlayer
 .content-collections
 .source
+/content/docs/
 
 # cache
 .cache/