fix(admin): city-scoped district pick and clearer overlap errors

Region partners only select districts under the chosen city; overlap errors name the occupying partner.

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

apps/admin-web/src/lib/china-region.ts

@@ -79,6 +79,33 @@ export function districtCodeToCityCode(districtCode: string): string {
   return `${districtCode.slice(0, 4)}00`;
 }
 
+export type DistrictOption = { value: string; label: string };
+
+/** 按开城城市 code（4 位或 6 位）取该市下区县列表 */
+export function getDistrictOptionsByCityCode(cityCode?: string | null): DistrictOption[] {
+  if (!cityCode?.trim()) return [];
+  const normalized = normalizeCityAdcode(cityCode.trim());
+  const prefix4 = normalized.slice(0, 4);
+
+  for (const province of regionData) {
+    for (const city of province.children ?? []) {
+      const cityValue = String(city.value);
+      const cityNorm = normalizeCityAdcode(cityValue);
+      if (cityNorm === normalized || cityValue === prefix4 || cityValue === cityCode.trim()) {
+        return (city.children ?? []).map((d) => ({
+          value: String(d.value),
+          label: String(d.label),
+        }));
+      }
+    }
+  }
+  return [];
+}
+
+export function districtCodeLabel(code: string): string {
+  return codeToText[code] || code;
+}
+
 export function parseRegionCodes(codes?: string[]): ParsedChinaRegion | null {
   if (!codes || codes.length < 3) return null;
   const [provinceCode, cityCode, districtCode] = codes;