feat: update documentation source and add index.md

- Changed documentation source from 'documentation.md' to 'index.md' in content.config.ts.
- Added new index.md file containing comprehensive documentation for ArtMCP, including installation, tools, prompts, resources, MCP integration, and API endpoints.
- Updated GitHub repository configuration in nuxt.config.ts for consistency.
- Bumped dependencies in package.json to latest versions for improved functionality and security.

app/pages/index.vue

@@ -1,5 +1,5 @@
 <script setup lang="ts">
-const { data: documentation } = await useAsyncData('documentation', () =>
+const { data: documentation } = await useAsyncData('index', () =>
   queryCollection('documentation').first()
 )
 </script>