Fix: Remove relatedPosts field causing KeyStatic error

The relationship field was causing "n.call is not a function" error.
Removed relatedPosts from both keystatic.config.ts and content.config.ts.

Other optimizations remain:
- Site singleton for global settings
- Brand mark (globe logo)
- Entry layout grouping
- Preview URL configuration
- Published and featured checkbox fields

Co-Authored-By: Claude <noreply@anthropic.com>

.gitignore

@@ -21,4 +21,6 @@ pnpm-debug.log*
 
 pnpm-lock.yaml
 
-.astro
+.astro
+# Local Netlify folder
+.netlify