feat(export): tailor content batch dialog and widen layout menu

src/pages/ExportPage.scss

@@ -143,7 +143,9 @@
     position: absolute;
     top: calc(100% + 6px);
     left: 0;
-    right: 0;
+    right: auto;
+    width: clamp(300px, 36vw, 420px);
+    max-width: calc(100vw - 40px);
     background: var(--bg-primary);
     border: 1px solid var(--border-color);
     border-radius: 12px;
@@ -1453,6 +1455,13 @@
   gap: 6px;
 }
 
+.format-note {
+  margin: 0 0 8px;
+  font-size: 12px;
+  line-height: 1.45;
+  color: var(--text-secondary);
+}
+
 .format-card {
   width: 100%;
   min-height: 0;