perf(app): throttle upload progress callbacks to 256KB steps

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

apps/mobile/android/app/src/main/kotlin/com/photolive/photo_live/UploadPutExecutor.kt

@@ -38,11 +38,15 @@ sealed class PutOutcome {
  * - 请求头：严格携带 Dart 传入的 credential.headers（Content-Type 经
  *   RequestBody.contentType 表达，Content-Length 由 okhttp 按声明长度
  *   发送，二者不重复注入）；
- * - 进度：写 body 驱动 [onProgress]（已发字节/总字节，IO 线程回调）；
+ * - 进度：写 body 驱动 [onProgress]（已发字节/总字节，IO 线程回调；
+ *   256KB 步长节流，末块必报 sent==total）；
  * - OkHttp 独立实例（4.12，与 Flutter 引擎无耦合；连接失败内置静默重试）。
  */
 object UploadPutExecutor {
 
+    /** 进度回调最小步长（字节）；末块必报。 */
+    private const val PROGRESS_STEP_BYTES = 256L * 1024
+
     private val defaultClient: OkHttpClient = OkHttpClient.Builder()
         .connectTimeout(Duration.ofSeconds(15))
         .writeTimeout(Duration.ofMinutes(3))
@@ -75,6 +79,7 @@ object UploadPutExecutor {
                 file.inputStream().use { input ->
                     val buffer = ByteArray(64 * 1024)
                     var sent = 0L
+                    var lastReported = 0L
                     while (true) {
                         val read = input.read(buffer)
                         if (read < 0) {
@@ -82,7 +87,10 @@ object UploadPutExecutor {
                         }
                         sink.write(buffer, 0, read)
                         sent += read
-                        onProgress?.invoke(sent, total)
+                        if (sent - lastReported >= PROGRESS_STEP_BYTES || sent == total) {
+                            lastReported = sent
+                            onProgress?.invoke(sent, total)
+                        }
                     }
                     sink.flush()
                 }