refactor: rename 'Releases' to 'Documentatie'

Changed terminology from release notes to feature documentation
to better reflect the continuous build-in-public approach.

Changes:
- Navigation: "Releases" → "Documentatie"
- Page titles: "Release Notes" → "Feature Documentatie"
- Metadata descriptions updated
- Timeline link text updated
- Sidebar heading updated
- Template and example docs updated

The /releases route remains the same for stability,
but all user-facing text now says "Documentatie".

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/(marketing)/releases/[category]/page.tsx

@@ -36,7 +36,7 @@ export async function generateMetadata({ params }: ReleasePageProps) {
   }
 
   return {
-    title: `${release.frontmatter.title} - Release Notes`,
+    title: `${release.frontmatter.title} - Documentatie`,
     description: release.frontmatter.description,
   }
 }