Performance & SEO optimization + Google login for CMS

Performance:
- Enable image optimization (Image: true, SVG: true)
- 429MB saved with WebP conversion

SEO:
- Add JSON-LD structured data (Organization & FAQ schemas)
- Add keywords and author metadata
- Update robots.txt with sitemap reference
- Add alt text to OpenGraph images

CMS:
- Enable Google OAuth login for admin panel
- Add logo to admin login page

Fixes:
- Update Telegram link to @ym1ktc on homepage

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

public/decapcms/config.yml

@@ -6,6 +6,10 @@ backend:
     - editor
   squash_merges: true
 
+# Identity widget for external OAuth providers (Google, GitHub, etc.)
+identity_widget:
+  enable: true
+
 media_folder: 'src/assets/images'
 public_folder: '/images'
 
@@ -14,6 +18,9 @@ locale: 'tr'
 site_url: https://radio.org.tr
 display_url: https://radio.org.tr
 
+# Logo for admin login page
+logo_url: https://radio.org.tr/_astro/ARC_2024_bayrak_logo-Large-1-1024x1024.png
+
 collections:
   - name: 'post'
     label: 'Blog Yazıları'
@@ -62,4 +69,4 @@ collections:
         required: false
       - label: 'İçerik'
         name: 'body'
-        widget: 'markdown'
+        widget: 'markdown'