refactor: manifest回归Release构建产物

- ota/目录删除(manifest是CI构建时动态生成上传)
- App URL改为Release下载路径(releases/download/...)
- 流程: CI build→生成manifest(SHA256动态)→上传Release
- Release #7: v0.1.0-dav-android-7-debug.apk + manifest.json

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

@@ -102,7 +102,7 @@ class MainActivity : AppCompatActivity() {
     }
 
     private fun manifestUrl(channel: String): String {
-        val base = "https://git.childish-ghost.com/LukeMackin/Yuzu-GCA/raw/branch/main/ota"
+        val base = "https://git.childish-ghost.com/LukeMackin/Yuzu-GCA/releases/download/v0.1.0-dav-android-7"
         return when (channel) {
             "beta" -> "$base/manifest-beta.json"
             "nightly" -> "$base/manifest-nightly.json"