refactor(gradle): 强制项目使用Java 7语法并统一API适配范围

- build.gradle: subprojects Java版本从11降级为1.7
- libwinboll/build.gradle: minSdkVersion从21统一为26
- build.properties: 编译计数器自动递增(buildCount: 23→24)

build.gradle

@@ -96,8 +96,8 @@ allprojects {
         // 1. 对纯 Java 模块的 JavaCompile 任务配置（升级为 Java 11）
         tasks.withType(JavaCompile) {
             options.compilerArgs << "-parameters"
-            sourceCompatibility = JavaVersion.VERSION_11
-            targetCompatibility = JavaVersion.VERSION_11
+            sourceCompatibility = JavaVersion.VERSION_1_7
+            targetCompatibility = JavaVersion.VERSION_1_7
             // 可选：确保编码一致
             options.encoding = "UTF-8"
         }