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

src/layouts/Layout.astro

@@ -35,6 +35,9 @@ const { language, textDirection } = I18N;
     <Metadata {...metadata} />
     <SiteVerification />
     <Analytics />
+    
+    <!-- Netlify Identity for Decap CMS -->
+    <script src="https://identity.netlify.com/v1/netlify-identity-widget.js"></script>
 
     <!-- Comment the line below to disable View Transitions -->
     <ClientRouter fallback="swap" />
@@ -44,5 +47,18 @@ const { language, textDirection } = I18N;
     <slot />
 
     <BasicScripts />
+    
+    <!-- Netlify Identity initialization -->
+    <script>
+      if (window.netlifyIdentity) {
+        window.netlifyIdentity.on("init", user => {
+          if (!user) {
+            window.netlifyIdentity.on("login", () => {
+              document.location.href = "/admin/";
+            });
+          }
+        });
+      }
+    </script>
   </body>
 </html>