refactor: remove unused collections and documentation files

- Deleted the 'index' and 'mcp' collections from content.config.ts.
- Removed the 'docs.md' file containing ArtMCP documentation.
- Deleted the 'index.md' file which served as a welcome page for ArtAPI.

content.config.ts

@@ -104,13 +104,5 @@ export default defineContentConfig({
       type: 'data',
       source: 'profile.md'
     }),
-    index: defineCollection({
-      type: 'page',
-      source: 'index.md'
-    }),
-    mcp: defineCollection({
-      type: 'page',
-      source: 'mcp.md'
-    })
   }
 })