Switch from GitHub Pages to Netlify deployment and fix CMS setup

- Remove GitHub Pages workflow (no longer needed)
- Update Decap CMS config with correct Netlify domain (taslak.radio.org.tr)
- Add comprehensive troubleshooting guide for 'Unable to access identity settings' error
- Provide step-by-step Netlify Identity and Git Gateway setup instructions
- Include verification steps and common issues resolution

The error occurs because Netlify Identity service needs to be enabled in the Netlify dashboard.

🤖 Generated with Claude Code

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

public/decapcms/config.yml

@@ -5,8 +5,8 @@ backend:
 media_folder: 'src/assets/images'
 public_folder: '/_astro'
 
-site_url: https://ym1ktc.github.io/ARC-Web-Sitesi
-display_url: https://ym1ktc.github.io/ARC-Web-Sitesi
+site_url: https://taslak.radio.org.tr
+display_url: https://taslak.radio.org.tr
 
 collections:
   - name: 'post'