Fix: Blog URLs and remove duplicate AI Automation links

Fixes:
1. Blog URLs now correct (without .md extension)
   - Changed from: /blog/core-web-vitals.md/
   - Changed to: /blog/core-web-vitals/
2. Fixed duplicate AI Automation in navigation
   - Removed duplicate from header submenu
   - Removed duplicate from mobile menu
   - Removed duplicate from footer
   - Now 4 unique services in all menus

Blog:
- getStaticPaths: slug.replace('.md', '')
- blog/index.astro: links use slug.replace('.md', '')
- Blog builds to correct URLs without .md

Navigation:
- Header submenu: 4 services (not 5)
- Mobile menu: 4 services (not 5)
- Footer: 4 services (was 5 with duplicate)

Services (4 unique):
1. พัฒนาเว็บไซต์
2. AI Automation
3. พัฒนาแอปพลิเคชัน
4. ที่ปรึกษาการตลาดออนไลน์

src/pages/blog/[slug].astro

@@ -5,7 +5,7 @@ import { getCollection } from 'astro:content';
 export async function getStaticPaths() {
   const posts = await getCollection('blog');
   return posts.map((post) => ({
-    params: { slug: post.id },
+    params: { slug: post.id.replace('.md', '') },
     props: { post },
   }));
 }

src/pages/blog/index.astro

@@ -26,14 +26,14 @@ posts.sort((a, b) => b.data.pubDate.valueOf() - a.data.pubDate.valueOf());
                 ))}
               </div>
               <h2 class="text-xl font-bold mb-3 hover:text-accent-blue transition">
-                <a href={`/blog/${post.id}/`} class="hover:underline">{post.data.title}</a>
+                <a href={`/blog/${post.id.replace('.md', '')}/`} class="hover:underline">{post.data.title}</a>
               </h2>
               <p class="text-gray-600 mb-4 line-clamp-3">{post.data.description}</p>
               <div class="flex items-center justify-between text-sm text-gray-500">
                 <span>{post.data.author}</span>
                 <span>{post.data.pubDate.toLocaleDateString('th-TH')}</span>
               </div>
-              <a href={`/blog/${post.id}/`} class="text-accent-blue font-medium hover:underline flex items-center gap-2 mt-4">อ่านเพิ่มเติม →</a>
+              <a href={`/blog/${post.id.replace('.md', '')}/`} class="text-accent-blue font-medium hover:underline flex items-center gap-2 mt-4">อ่านเพิ่มเติม →</a>
             </div>
           </article>
         ))}