feat: 优化语言切换下拉交互并支持玩法规则多语言内容

src/lib/play-rules-html.ts

@@ -0,0 +1,38 @@
+import { normalizeLanguage, type AppLanguage } from "@/i18n/language";
+
+const KEY_LEGACY = "frontend.play_rules_html";
+const KEY_ZH = "frontend.play_rules_html_zh";
+const KEY_EN = "frontend.play_rules_html_en";
+const KEY_NE = "frontend.play_rules_html_ne";
+
+type SettingItem = { key: string; value: unknown };
+
+function asNonEmptyString(value: unknown): string | null {
+  if (typeof value !== "string") {
+    return null;
+  }
+  const trimmed = value.trim();
+  return trimmed === "" ? null : trimmed;
+}
+
+/** 从 public settings 列表中按玩家语言选取玩法规则 HTML */
+export function resolvePlayRulesHtml(
+  items: SettingItem[],
+  language: string | undefined,
+): string | null {
+  const kv = new Map(items.map((item) => [item.key, item.value]));
+  const legacy = asNonEmptyString(kv.get(KEY_LEGACY));
+  const zh = asNonEmptyString(kv.get(KEY_ZH));
+  const en = asNonEmptyString(kv.get(KEY_EN));
+  const ne = asNonEmptyString(kv.get(KEY_NE));
+
+  const lang: AppLanguage = normalizeLanguage(language);
+
+  if (lang === "zh") {
+    return zh ?? legacy;
+  }
+  if (lang === "ne") {
+    return ne ?? en ?? zh ?? legacy;
+  }
+  return en ?? zh ?? legacy;
+}