fix: Home icon active state — exact match "/" instead of startsWith

matchPaths: ['/'] with startsWith('/') matched every route,
keeping Home highlighted on all pages.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/src/components/layout/Sidebar.tsx

@@ -160,7 +160,9 @@ export function Sidebar() {
   /* ── Active detection ─────────────────────────────── */
 
   const isActive = (item: NavEntry) => {
-    if (item.matchPaths) return item.matchPaths.some(p => location.pathname.startsWith(p))
+    if (item.matchPaths) return item.matchPaths.some(p =>
+      p === '/' ? location.pathname === '/' : location.pathname.startsWith(p)
+    )
     if (item.href === '/') return location.pathname === '/'
     return location.pathname.startsWith(item.href)
   }