feat: trim integration pages from 75 to 25 + migrate to MDX

- Add dedicatedPage flag to integration registry (25 true, 50 false)
- Delete hardcoded nextjs/react/vue/wordpress route pages (wrong metadata)
- Hub page routes non-dedicated integrations to /integrations/script-tag
- Add 301 redirects for 50 removed slugs → /integrations/script-tag
- Migrate guide content from TSX to MDX (content/integrations/*.mdx)
- Add gray-matter, next-mdx-remote, remark-gfm dependencies
- Add content loader (lib/integration-content.ts) matching ciphera-website pattern
- Add prebuild script for integration guide index generation
- Sitemap reduced from 83 to 35 URLs with real lastmod dates
- Remove seoDescription from registry (now in MDX frontmatter)

content/integrations/wordpress.mdx

@@ -0,0 +1,27 @@
+---
+title: "WordPress"
+description: "Add Pulse analytics to your WordPress site via a plugin or theme header code."
+category: "cms"
+brandColor: "#21759B"
+officialUrl: "https://wordpress.org/documentation"
+relatedIds: ["ghost", "drupal", "woocommerce"]
+date: "2026-03-28"
+---
+
+Add the Pulse script via a plugin or by editing your theme's header file directly.
+
+---
+
+## Method 1: Using a plugin (Recommended)
+
+The easiest way is to use the [WPCode (Insert Headers and Footers)](https://wordpress.org/plugins/insert-headers-and-footers/) plugin. Install it, then go to **Code Snippets -> Header & Footer** and paste the Pulse script into the Header section.
+
+<CodeBlock filename="Header Script">{`<script
+  defer
+  data-domain="your-site.com"
+  src="https://pulse.ciphera.net/script.js"
+></script>`}</CodeBlock>
+
+## Method 2: Edit header.php directly
+
+Go to **Appearance -> Theme File Editor** and edit `header.php`. Add the Pulse script before the closing `</head>` tag.