Add GitHub Pages deployment and Decap CMS support

- Add GitHub Actions workflow for automatic deployment to GitHub Pages
- Configure Decap CMS for Turkish blog post management
- Add Netlify Identity integration for authentication
- Create admin redirect page and routing
- Add comprehensive setup documentation
- Configure proper Turkish field labels and defaults
- Enable image uploads and media management

Site will now auto-deploy on every push to main branch.
Access CMS at: https://ym1ktc.github.io/ARC-Web-Sitesi/admin/

🤖 Generated with Claude Code

public/_redirects

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+/admin/* /decapcms/index.html 200