feat: add trading day split lines on hub market chart

Add toggle before technical indicators to show blue dashed vertical lines at Beijing 8:00 day boundaries.

Co-authored-by: Cursor <cursoragent@cursor.com>

manual_trading_hub/static/app.css

@@ -2831,6 +2831,34 @@ body.login-page {
   gap: 6px 10px;
 }
 
+.market-day-split-opt {
+  display: inline-flex;
+  align-items: center;
+  gap: 6px;
+  font-size: 0.72rem;
+  color: var(--muted);
+  cursor: pointer;
+  user-select: none;
+  padding: 2px 8px;
+  border-radius: 4px;
+  border: 1px solid var(--border-soft);
+  white-space: nowrap;
+}
+
+.market-day-split-opt:hover {
+  color: var(--text);
+  border-color: var(--border);
+}
+
+.market-day-split-opt input {
+  accent-color: #3b82f6;
+}
+
+.market-day-split-opt:has(input:checked) {
+  color: #3b82f6;
+  border-color: rgba(59, 130, 246, 0.45);
+}
+
 .market-ind-menu {
   position: relative;
   font-size: 0.72rem;