Add KeyStatic CMS integration

Features added:
- KeyStatic Core and Astro integration installed
- Markdoc integration for content rendering
- keystatic.config.ts with blog post schema
- Local storage mode for content management
- Conditional loading via SKIP_KEYSTATIC env var
- Netlify build command updated to skip KeyStatic in production

KeyStatic Admin UI available at:
- Local: http://localhost:4321/keystatic
- Production: Disabled for security

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

netlify.toml

@@ -1,6 +1,6 @@
 [build]
   publish = "dist"
-  command = "npm run build"
+  command = "SKIP_KEYSTATIC=true npm run build"
   ignore = "git log -1 --pretty=format:'%ae' | grep -v 'bcanata@hotmail.com'"
 [build.processing.html]
   pretty_urls = false