feat(ui): split downloads and history into tabs

public/style.css

@@ -552,11 +552,54 @@ body {
   word-break: break-word;
 }
 
+/* ===== Main Tabs ===== */
+.main-tabs {
+  max-width: 1200px;
+  margin: 16px auto 0;
+  padding: 0 16px;
+}
+
+.tab-bar {
+  display: flex;
+  gap: 4px;
+  border-bottom: 2px solid var(--border);
+  margin-bottom: 0;
+}
+
+.tab-btn {
+  background: none;
+  border: none;
+  border-bottom: 3px solid transparent;
+  margin-bottom: -2px;
+  padding: 10px 20px;
+  font-size: 0.95rem;
+  font-weight: 600;
+  color: var(--text-secondary);
+  cursor: pointer;
+  transition: color 0.2s, border-color 0.2s;
+  border-radius: 4px 4px 0 0;
+}
+
+.tab-btn:hover {
+  color: var(--text-primary);
+  background: var(--surface);
+}
+
+.tab-btn.active {
+  color: var(--accent);
+  border-bottom-color: var(--accent);
+  background: var(--surface);
+}
+
+.tab-panel {
+  padding-top: 0;
+}
+
 /* ===== Recently Completed History ===== */
 .history-container {
-  max-width: 1200px;
-  margin: 24px auto 0;
-  padding: 0 16px;
+  max-width: unset;
+  margin: 0;
+  padding: 0;
 }
 
 .history-header {