security: SHA256校验通过Android Bridge(Java侧计算)

- Bridge.sha256() 用 MessageDigest 计算
- JS下载后 Android.sha256(t) 比对 version.txt 哈希
- version.txt 恢复三列: ver|url|sha256
- 避免 Web Crypto API 在 file:// 域不可用问题

ota/version.txt

@@ -1 +1 @@
-0.1.0-dav-android-6|https://git.childish-ghost.com/LukeMackin/Yuzu-GCA/raw/branch/main/ota/h5/index-v6.html
+0.1.0-dav-android-6|https://git.childish-ghost.com/LukeMackin/Yuzu-GCA/raw/branch/main/ota/h5/index-v6.html|a53319e28c5b9ce5da6799d9b2fe547f4391386f23b68ac10814567edd445188

packages/client-android/android/app/src/main/java/dev/yuzu/gca/MainActivity.kt

@@ -48,6 +48,12 @@ class MainActivity : AppCompatActivity() {
             ctx.cacheFile.delete()
             Log.i(TAG, "Cache cleared")
         }
+        @android.webkit.JavascriptInterface
+        fun sha256(input: String): String {
+            val md = java.security.MessageDigest.getInstance("SHA-256")
+            val digest = md.digest(input.toByteArray(Charsets.UTF_8))
+            return digest.joinToString("") { "%02x".format(it) }
+        }
     }
 
     companion object { private const val TAG = "GCA-H5" }