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 },
   }));
 }