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/components/release-sidebar.tsx

@@ -82,7 +82,7 @@ export function ReleaseSidebar({ releases, metadata }: ReleaseSidebarProps) {
       <aside className="hidden lg:block w-64 fixed top-16 bottom-0 bg-white border-r border-slate-200 overflow-y-auto">
         <div className="p-6">
           <h2 className="text-xs font-semibold text-slate-500 uppercase tracking-wide mb-4">
-            Release Notes
+            Documentatie
           </h2>
 
           <nav className="space-y-1">