完善语言包占位符契约

将占位符提取规则扩展为全部花括号形式，按出现顺序校验数字、命名及空占位符。

ruoyi-admin/src/test/java/com/ruoyi/common/utils/BackendI18nBundleContractTest.java

@@ -22,7 +22,7 @@ class BackendI18nBundleContractTest {
             "messages_zh_CN.properties", "messages_zh_TW.properties",
             "messages_en_US.properties", "messages_vi.properties",
             "messages_th_TH.properties");
-    private static final Pattern PLACEHOLDER = Pattern.compile("\\{\\d+}");
+    private static final Pattern PLACEHOLDER = Pattern.compile("\\{[^{}]*}");
 
     @Test
     void everyLocalizedBundleHasTheSameNonBlankKeysAndPlaceholders() throws Exception {