feat(review-queue): MITRE update review queue for leads

- New /techniques/review-queue page: lists all techniques flagged for
  review after a MITRE ATT&CK sync, grouped by tactic. Leads and admins
  can mark each one reviewed inline without leaving the page.
- Sidebar: 'Review Queue' link (admin/red_lead/blue_lead only) with an
  amber badge showing the live pending count.
- TechniqueDetailPage: amber banner when review_required=true explaining
  what happened and who can act; 'Mark as Reviewed' button now amber
  coloured for visual distinction. 'Leads only' chip shown for blue_tech.

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

frontend/src/pages/TechniqueDetailPage.tsx

@@ -163,7 +163,7 @@ export default function TechniqueDetailPage() {
             <button
               onClick={() => reviewMutation.mutate()}
               disabled={reviewMutation.isPending}
-              className="flex items-center gap-2 rounded-lg bg-cyan-600 px-4 py-2 text-sm font-medium text-white hover:bg-cyan-500 disabled:opacity-50 transition-colors"
+              className="flex items-center gap-2 rounded-lg bg-amber-600 px-4 py-2 text-sm font-medium text-white hover:bg-amber-500 disabled:opacity-50 transition-colors shrink-0"
             >
               {reviewMutation.isPending ? (
                 <Loader2 className="h-4 w-4 animate-spin" />
@@ -176,6 +176,31 @@ export default function TechniqueDetailPage() {
         </div>
       </div>
 
+      {/* Review required banner */}
+      {technique.review_required && (
+        <div className="flex items-start gap-3 rounded-xl border border-amber-500/30 bg-amber-500/5 p-4">
+          <AlertTriangle className="mt-0.5 h-5 w-5 shrink-0 text-amber-400" />
+          <div className="flex-1 min-w-0">
+            <p className="text-sm font-medium text-amber-300">
+              This technique has been updated in MITRE ATT&CK
+            </p>
+            <p className="mt-0.5 text-xs text-amber-400/70">
+              The MITRE ATT&CK sync detected changes to this technique.
+              {technique.mitre_last_modified && (
+                <> Last modified in ATT&CK: <span className="font-mono">{technique.mitre_last_modified.slice(0, 10)}</span>.</>
+              )}
+              {" "}A lead or admin should review the changes and click{" "}
+              <span className="font-semibold">Mark as Reviewed</span> to acknowledge them.
+            </p>
+          </div>
+          {!canReview && (
+            <span className="shrink-0 rounded-full border border-amber-500/20 bg-amber-500/10 px-2 py-0.5 text-[10px] text-amber-400">
+              Leads only
+            </span>
+          )}
+        </div>
+      )}
+
       {/* Info Section */}
       <div className="grid gap-6 lg:grid-cols-3">
         {/* Description */}