Fix navigation active state - use exact match

Changed router-link-active to router-link-exact-active
to prevent Dashboard from being highlighted on all routes.

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

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

frontend/src/layouts/ClientLayout.vue

@@ -113,7 +113,7 @@ async function handleLogout() {
   color: white;
 }
 
-.nav-item.router-link-active {
+.nav-item.router-link-exact-active {
   background: #48bb78;
   color: white;
 }

frontend/src/layouts/SuperadminLayout.vue

@@ -111,7 +111,7 @@ async function handleLogout() {
   color: white;
 }
 
-.nav-item.router-link-active {
+.nav-item.router-link-exact-active {
   background: #667eea;
   color: white;
 }