feat(ST-359): add Solo nav link between Producten and Todos

- Active on /solo and /products/[id]/solo; Producten inactive when on solo pages
- Refactored navLinks to carry explicit active boolean for custom path matching

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

components/shared/nav-bar.tsx

@@ -26,8 +26,9 @@ export function NavBar({ isDemo, roles }: NavBarProps) {
   const productId = productMatch ? productMatch[1] : null
 
   const navLinks = [
-    { href: '/dashboard', label: 'Producten' },
-    { href: '/todos', label: "Todo's" },
+    { href: '/dashboard', label: 'Producten', active: pathname.startsWith('/dashboard') || pathname.startsWith('/products') && !pathname.includes('/solo') },
+    { href: '/solo', label: 'Solo', active: pathname.includes('/solo') },
+    { href: '/todos', label: "Todo's", active: pathname.startsWith('/todos') },
   ]
 
   return (
@@ -51,7 +52,7 @@ export function NavBar({ isDemo, roles }: NavBarProps) {
             href={link.href}
             className={cn(
               'px-3 py-1.5 rounded-md text-sm transition-colors',
-              pathname.startsWith(link.href)
+              link.active
                 ? 'bg-primary-container text-primary-container-foreground font-medium'
                 : 'text-muted-foreground hover:text-foreground hover:bg-surface-container'
             )}