chore: Android 正式签名配置 + 截图尺寸适配

- 生成 release.jks 正式签名密钥库
- build.gradle.kts 配置 release 签名自动读取 key.properties
- .gitignore 排除 keystore 和 key.properties
- 截图调整为 6.5 寸规格 (1242x2688)

Co-Authored-By: Claude <noreply@anthropic.com>

health_app/android/app/build.gradle.kts

@@ -5,6 +5,13 @@ plugins {
     id("dev.flutter.flutter-gradle-plugin")
 }
 
+// 加载正式签名配置
+val keystorePropertiesFile = rootProject.file("key.properties")
+val keystoreProperties = java.util.Properties()
+if (keystorePropertiesFile.exists()) {
+    keystoreProperties.load(keystorePropertiesFile.inputStream())
+}
+
 android {
     namespace = "com.datalumina.YYA"
     compileSdk = flutter.compileSdkVersion
@@ -20,21 +27,28 @@ android {
     }
 
     defaultConfig {
-        // TODO: Specify your own unique Application ID (https://developer.android.com/studio/build/application-id.html).
         applicationId = "com.datalumina.YYA"
-        // You can update the following values to match your application needs.
-        // For more information, see: https://flutter.dev/to/review-gradle-config.
         minSdk = flutter.minSdkVersion
         targetSdk = flutter.targetSdkVersion
         versionCode = flutter.versionCode
         versionName = flutter.versionName
     }
 
+    // 正式签名配置
+    signingConfigs {
+        create("release") {
+            if (keystorePropertiesFile.exists()) {
+                keyAlias = keystoreProperties["keyAlias"] as String?
+                keyPassword = keystoreProperties["keyPassword"] as String?
+                storeFile = keystoreProperties["storeFile"]?.let { file(it) }
+                storePassword = keystoreProperties["storePassword"] as String?
+            }
+        }
+    }
+
     buildTypes {
         release {
-            // TODO: Add your own signing config for the release build.
-            // Signing with the debug keys for now, so `flutter run --release` works.
-            signingConfig = signingConfigs.getByName("debug")
+            signingConfig = signingConfigs.getByName("release")
         }
     }
 }