docs: add VitePress documentation site

- 22 content pages across Guide, Concepts, and Reference sections
- Custom indigo/cyan theme with Lucide icons and Mermaid diagrams
- GitHub Actions workflow for GitHub Pages deployment
- Live preview: https://mempalace-docs.netlify.app/

website/.gitignore

@@ -0,0 +1,36 @@
+# dependencies (bun install)
+node_modules
+
+# output
+out
+dist
+.vitepress/dist
+.vitepress/.temp
+*.tgz
+
+# code coverage
+coverage
+*.lcov
+
+# logs
+logs
+*.log
+report.[0-9]_.[0-9]_.[0-9]_.[0-9]_.json
+
+# dotenv environment variable files
+.env
+.env.development.local
+.env.test.local
+.env.production.local
+.env.local
+
+# caches
+.eslintcache
+.cache
+*.tsbuildinfo
+
+# IntelliJ based IDEs
+.idea
+
+# Finder (MacOS) folder config
+.DS_Store