feat(seo): enhance seo and security configurations

- Remove static robots.txt and generate it dynamically during build
- Add security headers in vercel.json
- Improve structured data with BreadcrumbList and Course schema
- Make site URL dynamic based on deployment environment
- Enhance sitemap configuration with priority and changefreq

vercel.json

@@ -2,5 +2,50 @@
   "buildCommand": "npm run build",
   "installCommand": "npm install",
   "framework": "vitepress",
-  "outputDirectory": "docs/.vitepress/dist"
+  "outputDirectory": "docs/.vitepress/dist",
+  "headers": [
+    {
+      "source": "/(.*)",
+      "headers": [
+        {
+          "key": "X-Content-Type-Options",
+          "value": "nosniff"
+        },
+        {
+          "key": "X-Frame-Options",
+          "value": "DENY"
+        },
+        {
+          "key": "X-XSS-Protection",
+          "value": "1; mode=block"
+        },
+        {
+          "key": "Referrer-Policy",
+          "value": "strict-origin-when-cross-origin"
+        },
+        {
+          "key": "Permissions-Policy",
+          "value": "camera=(), microphone=(), geolocation=()"
+        }
+      ]
+    },
+    {
+      "source": "/sitemap.xml",
+      "headers": [
+        {
+          "key": "Cache-Control",
+          "value": "public, max-age=86400, s-maxage=86400"
+        }
+      ]
+    },
+    {
+      "source": "/robots.txt",
+      "headers": [
+        {
+          "key": "Cache-Control",
+          "value": "public, max-age=86400, s-maxage=86400"
+        }
+      ]
+    }
+  ]
 }