feat(web): add Knowledge Base page placeholder

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

apps/web/app/(dashboard)/knowledge-base/page.tsx

@@ -0,0 +1,10 @@
+export default function KnowledgeBasePage() {
+  return (
+    <div className="p-6">
+      <h1 className="text-2xl font-bold">Knowledge Base</h1>
+      <p className="mt-2 text-muted-foreground">
+        Your team&apos;s documents and references will appear here.
+      </p>
+    </div>
+  );
+}