feat: Enhance numbering rule service with separator handling

- Introduced functionality to extract and manage individual separators for numbering rule parts.
- Added methods to join parts with their respective separators, improving code generation flexibility.
- Updated the numbering rule service to utilize the new separator logic during part processing.
- Enhanced the frontend components to support custom separators for each part, allowing for more granular control over numbering formats.

frontend/components/numbering-rule/NumberingRuleCard.tsx

@@ -25,7 +25,7 @@ export const NumberingRuleCard: React.FC<NumberingRuleCardProps> = ({
   isPreview = false,
 }) => {
   return (
-    <Card className="border-border bg-card">
+    <Card className="border-border bg-card flex-1">
       <CardHeader className="pb-3">
         <div className="flex items-center justify-between">
           <Badge variant="outline" className="text-xs sm:text-sm">