fix: PDF 문제 분리 메뉴 위치 개선 — 문제집 바로 아래로 이동 + 문제집 페이지에 진입 버튼 추가

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

frontend/src/app/exams/page.tsx

@@ -218,6 +218,10 @@ function ExamsBody() {
               <Icon name="file-pdf" size={14} />
               PDF 업로드
             </Button>
+            <Button type="button" $variant="primary" $size="sm" onClick={() => router.push('/study/import-pdf')}>
+              <Icon name="file-pdf" size={14} />
+              PDF 문제 분리
+            </Button>
           </ActionButtons>
         </ActionCard>
       </ActionRow>

frontend/src/components/layout/SideNav.tsx

@@ -35,6 +35,12 @@ const BASE_NAV_ITEMS: Array<{
     match: (pathname) =>
       pathname.startsWith('/exams') || pathname.startsWith('/study/exam'),
   },
+  {
+    href: '/study/import-pdf',
+    label: 'PDF 문제 분리',
+    icon: 'file-pdf',
+    match: (pathname) => pathname.startsWith('/study/import-pdf'),
+  },
   {
     href: '/review',
     label: '복습',
@@ -54,12 +60,6 @@ const BASE_NAV_ITEMS: Array<{
     icon: 'folders',
     match: (pathname) => pathname.startsWith('/subjects'),
   },
-  {
-    href: '/study/import-pdf',
-    label: 'PDF 가져오기',
-    icon: 'file-pdf',
-    match: (pathname) => pathname.startsWith('/study/import-pdf'),
-  },
   {
     href: '/pricing',
     label: '플랜',