build(android): 接入正式签名配置 + 版本号改为 1.1.0-dev.1 (2)

- app/build.gradle.kts 读取 android/key.properties（不存在时回退 debug keystore）
- .gitignore 忽略 key.properties / keystore / *.jks
- pubspec: version 1.1.0-dev.1+2

注意：key.properties 与 keystore 文件由开发者本地生成，不入库。
生成后 flutter build apk --release 即为正式签名包。

pubspec.yaml

@@ -16,7 +16,7 @@ publish_to: 'none' # Remove this line if you wish to publish to pub.dev
 # https://developer.apple.com/library/archive/documentation/General/Reference/InfoPlistKeyReference/Articles/CoreFoundationKeys.html
 # In Windows, build-name is used as the major, minor, and patch parts
 # of the product and file versions while build-number is used as the build suffix.
-version: 1.1.0+1
+version: 1.1.0-dev.1+2
 
 environment:
   sdk: ^3.0.0