feat(frontend): translate UI to English and refresh layout styles

src/index.css

@@ -64,6 +64,124 @@
 
 body {
   margin: 0;
+  background: linear-gradient(180deg, rgba(170, 59, 255, 0.08), transparent 220px) no-repeat var(--bg);
+}
+
+a {
+  color: var(--accent);
+  text-decoration: none;
+}
+
+a:hover {
+  text-decoration: underline;
+}
+
+.app-shell {
+  display: grid;
+  grid-template-columns: 240px 1fr;
+  min-height: 100vh;
+}
+
+.sidebar {
+  border-right: 1px solid var(--border);
+  padding: 20px 16px;
+  text-align: left;
+  background: color-mix(in srgb, var(--bg) 94%, var(--accent) 6%);
+}
+
+.sidebar-title {
+  margin: 0 0 14px;
+}
+
+.sidebar-nav {
+  display: grid;
+  gap: 10px;
+}
+
+.sidebar-session {
+  margin-top: 20px;
+  font-size: 13px;
+}
+
+.page-content {
+  padding: 18px;
+  text-align: left;
+}
+
+.panel {
+  border: 1px solid var(--border);
+  border-radius: 12px;
+  padding: 16px;
+  box-shadow: var(--shadow);
+  background: var(--bg);
+}
+
+.form-grid {
+  display: grid;
+  gap: 10px;
+}
+
+.row-wrap {
+  display: flex;
+  gap: 8px;
+  flex-wrap: wrap;
+}
+
+.input {
+  border: 1px solid var(--border);
+  border-radius: 8px;
+  padding: 8px 10px;
+  min-width: 120px;
+  background: transparent;
+  color: var(--text-h);
+}
+
+.input:focus {
+  outline: 2px solid var(--accent-border);
+  outline-offset: 1px;
+}
+
+.btn {
+  border: 1px solid var(--accent-border);
+  background: var(--accent);
+  color: #fff;
+  border-radius: 8px;
+  padding: 8px 12px;
+  cursor: pointer;
+}
+
+.btn-secondary {
+  background: transparent;
+  color: var(--text-h);
+}
+
+.btn-danger {
+  background: #dc2626;
+  border-color: #dc2626;
+}
+
+.muted {
+  color: var(--text);
+}
+
+.error-text {
+  color: #dc2626;
+  margin-top: 10px;
+}
+
+.list-reset {
+  list-style: none;
+  padding: 0;
+  margin: 0;
+}
+
+.card {
+  border: 1px solid var(--border);
+  border-radius: 10px;
+  padding: 10px;
+  display: grid;
+  gap: 8px;
+  background: color-mix(in srgb, var(--bg) 95%, var(--accent) 5%);
 }
 
 h1,