refactor: rename /releases route to /documentatie

Complete route rename from /releases to /documentatie to better reflect
the continuous build-in-public nature of the project (not formal releases).

Changes:
- Renamed app/(marketing)/releases/ → app/(marketing)/documentatie/
- Renamed content/nl/releases/ → content/nl/documentatie/
- Updated all internal links from /releases to /documentatie
- Updated middleware publicRoutes (/releases → /documentatie)
- Updated navigation.json link
- Updated build-timeline.tsx documentation link
- Updated all component href attributes
- Updated lib/mdx/releases.ts content directory path
- Updated sidebar component paths and checks
- Updated MDX documentation files with new routes

Files changed:
- app/(marketing)/documentatie/[category]/page.tsx (footer link)
- app/(marketing)/documentatie/page.tsx (card links)
- app/(marketing)/documentatie/components/release-sidebar.tsx (all links)
- app/(marketing)/components/build-timeline.tsx (documentation link)
- content/nl/navigation.json (header link)
- content/nl/documentatie/*.mdx (internal references)
- middleware.ts (publicRoutes)
- lib/mdx/releases.ts (RELEASES_DIR path)

This prevents future confusion between "releases" (versioned software releases)
and "documentatie" (continuous build documentation).

Old URL: /releases/[category]
New URL: /documentatie/[category]

The old /releases route now returns 404 as expected.

app/(marketing)/documentatie/layout.tsx

@@ -0,0 +1,34 @@
+/**
+ * Releases Layout
+ *
+ * Layout for release notes pages with sidebar navigation
+ */
+
+import type { ReactNode } from 'react'
+import { getAllReleases, getCategoryMetadata } from '@/lib/mdx/releases'
+import ReleaseSidebar from './components/release-sidebar-wrapper'
+
+interface ReleasesLayoutProps {
+  children: ReactNode
+}
+
+export default async function ReleasesLayout({ children }: ReleasesLayoutProps) {
+  const releases = await getAllReleases()
+  const metadata = await getCategoryMetadata()
+
+  return (
+    <div className="min-h-screen bg-slate-50">
+      <div className="max-w-[1400px] mx-auto">
+        <div className="flex">
+          {/* Sidebar - hidden on mobile, fixed on desktop */}
+          <ReleaseSidebar releases={releases} metadata={metadata} />
+
+          {/* Main Content */}
+          <div className="flex-1 lg:ml-64">
+            {children}
+          </div>
+        </div>
+      </div>
+    </div>
+  )
+}