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)

lib/integration-content.ts

@@ -0,0 +1,63 @@
+import fs from 'fs'
+import path from 'path'
+import matter from 'gray-matter'
+
+const CONTENT_DIR = path.join(process.cwd(), 'content', 'integrations')
+
+export interface IntegrationGuideMeta {
+  slug: string
+  title: string
+  description: string
+  category: string
+  brandColor: string
+  officialUrl: string
+  relatedIds: string[]
+  date: string
+}
+
+export interface IntegrationGuideArticle extends IntegrationGuideMeta {
+  content: string
+}
+
+export function getIntegrationGuides(): IntegrationGuideMeta[] {
+  if (!fs.existsSync(CONTENT_DIR)) return []
+
+  const files = fs.readdirSync(CONTENT_DIR).filter((f) => f.endsWith('.mdx'))
+
+  return files.map((filename) => {
+    const slug = filename.replace(/\.mdx$/, '')
+    const raw = fs.readFileSync(path.join(CONTENT_DIR, filename), 'utf-8')
+    const { data } = matter(raw)
+
+    return {
+      slug,
+      title: data.title,
+      description: data.description,
+      category: data.category,
+      brandColor: data.brandColor,
+      officialUrl: data.officialUrl,
+      relatedIds: data.relatedIds || [],
+      date: data.date,
+    }
+  })
+}
+
+export function getIntegrationGuide(slug: string): IntegrationGuideArticle | null {
+  const filePath = path.join(CONTENT_DIR, `${slug}.mdx`)
+  if (!fs.existsSync(filePath)) return null
+
+  const raw = fs.readFileSync(filePath, 'utf-8')
+  const { data, content } = matter(raw)
+
+  return {
+    slug,
+    title: data.title,
+    description: data.description,
+    category: data.category,
+    brandColor: data.brandColor,
+    officialUrl: data.officialUrl,
+    relatedIds: data.relatedIds || [],
+    date: data.date,
+    content,
+  }
+}