♻️ Restructure: Move Astro to repository root

BREAKING CHANGE: Astro project is now at repository root
- Removed dealplustech-astro subdirectory
- Moved all Astro files to root
- Updated PostCSS config to .cjs
- Removed old Next.js files

✅ 11 pages built successfully
✅ Cookie consent banner included
✅ Privacy/Terms links in footer
✅ Ready for Easypanel deployment (no root dir needed)

Migration path:
- Old structure: /dealplustech-astro/
- New structure: / (root)

public/manifest.json

@@ -1,26 +0,0 @@
-{
-  "name": "Deal Plus Tech",
-  "short_name": "DPT",
-  "description": "ผู้เชี่ยวชาญด้านระบบน้ำ จำหน่ายท่อ PPR, ท่อ HDPE, รั้วตาข่าย, อุปกรณ์ท่อน้ำ",
-  "start_url": "/",
-  "display": "standalone",
-  "background_color": "#ffffff",
-  "theme_color": "#1e40af",
-  "orientation": "portrait-primary",
-  "icons": [
-    {
-      "src": "/favicon-512.jpg",
-      "sizes": "512x512",
-      "type": "image/jpeg",
-      "purpose": "any maskable"
-    },
-    {
-      "src": "/favicon-512.jpg",
-      "sizes": "192x192",
-      "type": "image/jpeg"
-    }
-  ],
-  "categories": ["business", "shopping"],
-  "lang": "th",
-  "dir": "ltr"
-}