Merge branch 'claude/great-wiles-945b3f': 로그인 brand-divider 호흡 애니메이션 추가

5초 주기 ease-in-out으로 48px → 100% → 48px 너비가 반복되는
divider-breathe 키프레임 애니메이션을 적용.

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

app/static/styles.css

@@ -151,6 +151,13 @@ a { color: inherit; text-decoration: none; }
   background: var(--blue);
   border-radius: 2px;
   margin-top: 28px;
+  animation: divider-breathe 5s ease-in-out infinite;
+}
+
+@keyframes divider-breathe {
+  0%   { width: 48px; }
+  50%  { width: 100%; }
+  100% { width: 48px; }
 }
 
 .brand-footer {