feat(analytics): add blog engagement, ToC tracking, and 404 monitoring

- Added BlogEngagementTracker for reading time and completion tracking
- Added ToC click tracking in blog posts
- Added global 404 error monitoring in not-found.tsx
- Completed 'Total Transparency' suite

app/[locale]/blog/[slug]/page.tsx

@@ -11,6 +11,7 @@ import TableOfContents from '@/components/blog/TableOfContents';
 import { mdxComponents } from '@/components/blog/MDXComponents';
 import { Heading } from '@/components/ui';
 import { setRequestLocale } from 'next-intl/server';
+import BlogEngagementTracker from '@/components/analytics/BlogEngagementTracker';
 
 interface BlogPostProps {
   params: Promise<{
@@ -67,6 +68,12 @@ export default async function BlogPost({ params }: BlogPostProps) {
 
   return (
     <article className="bg-white min-h-screen font-sans selection:bg-primary/10 selection:text-primary">
+      <BlogEngagementTracker
+        title={post.frontmatter.title}
+        slug={slug}
+        category={post.frontmatter.category}
+        readingTime={getReadingTime(post.content)}
+      />
       {/* Featured Image Header */}
       {post.frontmatter.featuredImage ? (
         <div className="relative w-full h-[70vh] min-h-[500px] overflow-hidden group">