feat(export): simplify concurrency selector

src/components/Export/ExportDefaultsSettingsForm.scss

@@ -225,6 +225,37 @@
     color: var(--text-secondary);
   }
 
+  .concurrency-inline-options {
+    width: 100%;
+    display: grid;
+    grid-template-columns: repeat(6, minmax(0, 1fr));
+    gap: 6px;
+    margin-bottom: 10px;
+  }
+
+  .concurrency-option {
+    border: 1px solid var(--border-color);
+    border-radius: 10px;
+    min-height: 38px;
+    padding: 0;
+    background: var(--bg-primary);
+    color: var(--text-primary);
+    font-size: 14px;
+    font-weight: 600;
+    cursor: pointer;
+    transition: border-color 0.2s ease, background 0.2s ease, color 0.2s ease;
+
+    &:hover {
+      border-color: var(--text-tertiary);
+    }
+
+    &.active {
+      border-color: var(--primary);
+      background: rgba(var(--primary-rgb), 0.08);
+      color: var(--primary);
+    }
+  }
+
   .switch {
     position: relative;
     display: inline-flex;
@@ -323,6 +354,11 @@
       margin-bottom: 0;
     }
 
+    .concurrency-inline-options {
+      max-width: 360px;
+      margin-bottom: 0;
+    }
+
     .format-grid {
       max-width: 360px;
       margin-bottom: 0;
@@ -344,6 +380,7 @@
     .select-field,
     .settings-time-range-field,
     .log-toggle-line,
+    .concurrency-inline-options,
     .format-grid {
       max-width: none;
     }