Enable KeyStatic CMS for production

Changes:
- Added Netlify adapter for server-side rendering
- Changed output mode from static to server
- Updated KeyStatic storage from local to GitHub
- Removed SKIP_KEYSTATIC from Netlify build
- KeyStatic Admin UI will be available at /keystatic

Features:
- Server-side rendering with Netlify Functions
- GitHub integration for content management
- Production-ready KeyStatic Admin UI

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

keystatic.config.ts

@@ -2,7 +2,9 @@ import { config, fields, collection } from '@keystatic/core';
 
 export default config({
   storage: {
-    kind: 'local',
+    kind: 'github',
+    repo: 'YM1KTC/ARC-Web-Sitesi',
+    branch: 'main',
   },
   collections: {
     post: collection({