ui: redesign login lobby, fix auth view transition timing

internal/webapp/static/styles.css

@@ -44,7 +44,7 @@ select {
 }
 
 .workspace {
-  display: grid;
+  display: none;
   grid-template-columns: minmax(260px, 320px) minmax(360px, 1fr) minmax(280px, 360px);
   gap: 1px;
   min-height: 100vh;
@@ -464,27 +464,94 @@ button.is-loading .btn-spinner {
   justify-content: center;
   min-height: 100vh;
   padding: 28px;
-  background: var(--bg);
+  background: linear-gradient(160deg, #f5f7f4 0%, #e8efe5 100%);
 }
 
 .login-card {
   background: var(--surface);
   border: 1px solid var(--line);
-  border-radius: 12px;
-  padding: 44px 36px;
-  max-width: 420px;
+  border-radius: 18px;
+  padding: 52px 40px 44px;
+  max-width: 440px;
   width: 100%;
   text-align: center;
+  box-shadow: 0 12px 40px rgba(24, 32, 27, 0.07);
+}
+
+.login-card .eyebrow {
+  display: inline-block;
+  letter-spacing: 0.14em;
+  font-size: 11px;
+  text-transform: uppercase;
+  color: var(--accent);
+  font-weight: 750;
+  margin-bottom: 10px;
+}
+
+html[lang="ko"] .login-card .eyebrow {
+  text-transform: none;
+  letter-spacing: 0.04em;
 }
 
 .login-card h1 {
-  font-size: clamp(32px, 5vw, 52px);
-  margin: 14px 0 18px;
+  font-size: clamp(34px, 5.5vw, 56px);
+  margin: 8px 0 18px;
+  line-height: 1.05;
 }
 
 .login-card .lede {
-  margin: 0 auto 28px;
-  max-width: 34ch;
+  margin: 0 auto 32px;
+  max-width: 32ch;
+  color: var(--muted);
+  font-size: 15px;
+  line-height: 1.55;
+}
+
+.login-divider {
+  height: 1px;
+  background: var(--line);
+  margin: 28px 0 24px;
+  position: relative;
+}
+
+.login-divider::before {
+  content: attr(data-label);
+  position: absolute;
+  top: 50%;
+  left: 50%;
+  transform: translate(-50%, -50%);
+  background: var(--surface);
+  padding: 0 12px;
+  color: var(--muted);
+  font-size: 11px;
+  letter-spacing: 0.08em;
+  text-transform: uppercase;
+}
+
+.login-legal {
+  margin-top: 18px;
+  font-size: 12px;
+  color: var(--muted);
+  line-height: 1.5;
+}
+
+.login-legal a {
+  color: var(--muted);
+  text-decoration: underline;
+  text-underline-offset: 2px;
+}
+
+.login-error {
+  margin-top: 14px;
+  padding: 10px 14px;
+  border-radius: 8px;
+  background: var(--weak-bg);
+  color: var(--weak);
+  font-size: 13px;
+  display: none;
+}
+.login-error.visible {
+  display: block;
 }
 
 .user-bar {