주식 잔고, 주문 창 업그레이드

- 잔고, 주문 창 분리
 - full-width 섹션으로 쌓게 변경

src/pages/stock/Stock.css

@@ -325,6 +325,87 @@
     color: var(--muted);
 }
 
+.stock-trade {
+    display: grid;
+    gap: 16px;
+}
+
+.stock-balance {
+    display: grid;
+    gap: 12px;
+}
+
+.stock-balance__summary {
+    display: grid;
+    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
+    gap: 10px;
+}
+
+.stock-balance__card {
+    border: 1px solid var(--line);
+    border-radius: 14px;
+    padding: 10px;
+    display: grid;
+    gap: 6px;
+    background: rgba(0, 0, 0, 0.2);
+    font-size: 12px;
+    color: var(--muted);
+}
+
+.stock-balance__card strong {
+    font-size: 16px;
+    color: var(--text);
+}
+
+.stock-holdings {
+    display: grid;
+    gap: 8px;
+}
+
+.stock-holdings__item {
+    border: 1px solid var(--line);
+    border-radius: 12px;
+    padding: 10px;
+    display: grid;
+    grid-template-columns: minmax(0, 1.1fr) repeat(2, minmax(0, 0.7fr));
+    gap: 10px;
+    font-size: 12px;
+    color: var(--muted);
+    background: rgba(255, 255, 255, 0.02);
+}
+
+.stock-holdings__name {
+    margin: 0;
+    font-weight: 600;
+    color: var(--text);
+}
+
+.stock-holdings__code {
+    font-size: 11px;
+}
+
+.stock-order {
+    display: grid;
+    gap: 10px;
+}
+
+.stock-order label {
+    display: grid;
+    gap: 6px;
+    font-size: 12px;
+    color: var(--muted);
+}
+
+.stock-order input,
+.stock-order select {
+    border: 1px solid var(--line);
+    border-radius: 12px;
+    padding: 10px 12px;
+    background: rgba(0, 0, 0, 0.25);
+    color: var(--text);
+    outline: none;
+}
+
 @media (max-width: 900px) {
     .stock-header {
         grid-template-columns: 1fr;