Add SEO improvements: sitemap, robots.txt, LocalBusiness schema, GA4, llm.txt

- Add dynamic sitemap.xml generation for all pages
- Add robots.txt for search engine crawl directives
- Add LocalBusiness JSON-LD schema for local SEO
- Add BreadcrumbList schema for navigation breadcrumbs
- Add canonical URLs to all product pages
- Add Twitter Cards metadata
- Add Google Analytics 4 integration component
- Create llm.txt with all product data for AI optimization
- Create reusable UI components (Button, Card, Badge)
- Update company address to full Thai address
- Update .env.example with GA4 placeholder

.env.example

@@ -4,6 +4,28 @@
 # Site Configuration
 NEXT_PUBLIC_SITE_URL=https://dealplustech.co.th
 
+# Contact Information
+NEXT_PUBLIC_PHONE=090-555-1415
+NEXT_PUBLIC_EMAIL=info@dealplustech.co.th
+NEXT_PUBLIC_LINE_ID=@dealplustech
+NEXT_PUBLIC_FACEBOOK_URL=https://facebook.com/dealplustech
+
+# Company Information
+NEXT_PUBLIC_COMPANY_ADDRESS=บริษัท ดีล พลัส เทค จำกัด 9/70 ซอยนครลุง 17 แขวงบางไผ่ เขตบางแค กทม. 10160
+
+# Google Analytics 4 (Required for tracking)
+NEXT_PUBLIC_GA_MEASUREMENT_ID=G-XXXXXXXXXX
+
+# Google Search Console Verification (optional)
+# NEXT_PUBLIC_GOOGLE_SITE_VERIFICATION=your-verification-code
+
+# WordPress API (optional - for blog integration)
+# NEXT_PUBLIC_WORDPRESS_API_URL=https://your-wordpress-site.com/wp-json/wp/v2
+# Copy this file to .env.local and fill in the values
+
+# Site Configuration
+NEXT_PUBLIC_SITE_URL=https://dealplustech.co.th
+
 # Contact Information
 NEXT_PUBLIC_PHONE=090-555-1415
 NEXT_PUBLIC_EMAIL=dealplustech@gmail.com