feat(sidebar): add Techniques page to menu under ATT&CK group

/techniques (technique browser with filters) was an orphaned route —
only reachable via 'Back to techniques' button or direct URL.
Now exposed in the sidebar as part of a new ATT&CK group:
  ATT&CK ▾
    Techniques       → /techniques
    Coverage Matrix  → /matrix
    Review Queue     → /techniques/review-queue (leads+admin only)

Child role filtering added to SidebarLink.
Review Queue badge moved to the ATT&CK group header.

frontend/src/components/Sidebar.tsx

@@ -16,6 +16,7 @@ import {
   Crosshair,
   Zap,
   Grid3X3,
+  List,
   Gauge,
   ShieldCheck,
   GitCompareArrows,
@@ -37,8 +38,16 @@ interface NavItem {
 const mainLinks: NavItem[] = [
   { to: "/dashboard", label: "Dashboard", icon: LayoutDashboard },
   { to: "/executive-dashboard", label: "Executive Dashboard", icon: Gauge, roles: ["admin", "red_lead", "blue_lead", "viewer"] },
-  { to: "/matrix", label: "ATT&CK Matrix", icon: Grid3X3 },
-  { to: "/techniques/review-queue", label: "Review Queue", icon: ClipboardCheck, roles: ["admin", "red_lead", "blue_lead"] },
+  {
+    to: "/matrix",
+    label: "ATT&CK",
+    icon: Grid3X3,
+    children: [
+      { to: "/techniques", label: "Techniques", icon: List },
+      { to: "/matrix",     label: "Coverage Matrix", icon: Grid3X3 },
+      { to: "/techniques/review-queue", label: "Review Queue", icon: ClipboardCheck, roles: ["admin", "red_lead", "blue_lead"] },
+    ],
+  },
   {
     to: "/tests",
     label: "Tests",
@@ -66,8 +75,18 @@ const systemLinks: NavItem[] = [
 
 function SidebarLink({ item, badge }: { item: NavItem; badge?: number }) {
   const [expanded, setExpanded] = useState(false);
+  const { user } = useAuth();
+  const role = user?.role ?? "";
+  const isAdmin = role === "admin";
+
+  const childCanSee = (child: NavItem) => {
+    if (!child.roles) return true;
+    if (isAdmin) return true;
+    return child.roles.includes(role);
+  };
 
   if (item.children) {
+    const visibleChildren = item.children.filter(childCanSee);
     return (
       <div>
         <button
@@ -78,11 +97,18 @@ function SidebarLink({ item, badge }: { item: NavItem; badge?: number }) {
             <item.icon className="h-5 w-5" />
             {item.label}
           </span>
-          <ChevronDown className={`h-4 w-4 transition-transform ${expanded ? "rotate-180" : ""}`} />
+          <span className="flex items-center gap-1.5">
+            {badge !== undefined && badge > 0 && (
+              <span className="rounded-full bg-amber-500 px-1.5 py-0.5 text-[10px] font-bold text-white leading-none">
+                {badge}
+              </span>
+            )}
+            <ChevronDown className={`h-4 w-4 transition-transform ${expanded ? "rotate-180" : ""}`} />
+          </span>
         </button>
         {expanded && (
           <div className="ml-4 mt-1 space-y-0.5 border-l border-gray-800 pl-3">
-            {item.children.map((child) => (
+            {visibleChildren.map((child) => (
               <NavLink
                 key={child.to + child.label}
                 to={child.to}
@@ -168,7 +194,7 @@ export default function Sidebar() {
           <SidebarLink
             key={item.to + item.label}
             item={item}
-            badge={item.to === "/techniques/review-queue" ? reviewCount : undefined}
+            badge={item.label === "ATT&CK" ? reviewCount : undefined}
           />
         ))}