fix(android): 修复 markPartyReady 重试逻辑的循环退出Bug [CRITICAL]

## 发现的新Bug（从用户日志）

```
16:19:03.667 Successfully marked party ready on attempt 2  ✅
16:19:03.716 markPartyReady attempt 3 failed: cannot transition to ready status  ❌
16:19:03.731 markPartyReady attempt 4 failed: cannot transition to ready status  ❌
16:19:03.749 markPartyReady attempt 5 failed: cannot transition to ready status  ❌
16:19:03.750 Cancelled job: progress_collection  💀
```

## 根本原因

Kotlin `repeat` 的陷阱：
- `return@repeat` 只是跳过当前迭代
- **不会退出整个循环**
- 导致第2次成功后，第3、4、5次继续执行
- 服务器返回 "already ready, cannot transition"
- 第5次失败，代码认为所有尝试都失败，停止 keygen

## 修复内容

在每次迭代开始时检查成功标志：
```kotlin
repeat(5) { attempt ->
    if (markReadySuccess) return@repeat  // ← 添加这一行！

    val markReadyResult = grpcClient.markPartyReady(sessionId, partyId)
    if (markReadyResult.isSuccess) {
        markReadySuccess = true
        return@repeat
    }
    ...
}
```

现在流程：
- 第1次：optimistic lock conflict → 延迟重试
- 第2次：成功 → 设置标志 → return@repeat
- 第3次：检查标志已成功 → 立即 return@repeat（跳过）
- 第4次：检查标志已成功 → 立即 return@repeat（跳过）
- 第5次：检查标志已成功 → 立即 return@repeat（跳过）
- 循环结束 → 检查标志 = true → 继续执行 keygen ✅

## 影响范围

修复了所有 markPartyReady 重试位置（6处）：
- startKeygenAsInitiator
- joinKeygenViaGrpc
- startSignAsInitiator
- joinSignViaGrpc
- startSignAsJoiner
- 其他相关函数

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

backend/mpc-system/services/service-party-android/app/src/main/java/com/durian/tssparty/data/repository/TssRepository.kt

@@ -1345,10 +1345,14 @@ class TssRepository @Inject constructor(
             _sessionStatus.value = SessionStatus.IN_PROGRESS
 
             // Mark ready - with retry on optimistic lock conflict
+            var markReadySuccess = false
             repeat(5) { attempt ->
+                if (markReadySuccess) return@repeat  // Already succeeded, skip remaining attempts
+
                 val markReadyResult = grpcClient.markPartyReady(sessionId, partyId)
                 if (markReadyResult.isSuccess) {
                     android.util.Log.d("TssRepository", "markPartyReady successful on attempt ${attempt + 1}")
+                    markReadySuccess = true
                     return@repeat
                 }
                 val error = markReadyResult.exceptionOrNull()
@@ -1359,6 +1363,14 @@ class TssRepository @Inject constructor(
                 }
             }
 
+            // Check if any attempt succeeded
+            if (!markReadySuccess) {
+                android.util.Log.e("TssRepository", "All markPartyReady attempts failed")
+                stopProgressCollection()
+                _sessionStatus.value = SessionStatus.FAILED
+                return@coroutineScope Result.failure(Exception("Failed to mark party ready after 5 attempts"))
+            }
+
             // Wait for keygen result
             val keygenResult = tssNativeBridge.waitForKeygenResult(password)
             if (keygenResult.isFailure) {
@@ -2149,6 +2161,8 @@ class TssRepository @Inject constructor(
             // Mark ready - with retry on optimistic lock conflict
             var markReadySuccess = false
             repeat(5) { attempt ->
+                if (markReadySuccess) return@repeat  // Already succeeded, skip remaining attempts
+
                 val markReadyResult = grpcClient.markPartyReady(sessionId, partyId)
                 if (markReadyResult.isSuccess) {
                     android.util.Log.d("TssRepository", "Successfully marked party ready on attempt ${attempt + 1}")
@@ -2162,19 +2176,15 @@ class TssRepository @Inject constructor(
                     if (error?.message?.contains("optimistic lock conflict") == true && attempt < 4) {
                         android.util.Log.d("TssRepository", "Optimistic lock conflict detected, retrying after ${(attempt + 1) * 500}ms...")
                         delay((attempt + 1) * 500L)  // 500ms, 1s, 1.5s, 2s
-                    } else if (attempt == 4) {
-                        // Last attempt failed, return error
-                        stopProgressCollection()
-                        _sessionStatus.value = SessionStatus.FAILED
-                        return@coroutineScope Result.failure(Exception("Failed to mark party ready after 5 attempts: ${error?.message}"))
                     }
                 }
             }
 
             if (!markReadySuccess) {
+                android.util.Log.e("TssRepository", "All markPartyReady attempts failed")
                 stopProgressCollection()
                 _sessionStatus.value = SessionStatus.FAILED
-                return@coroutineScope Result.failure(Exception("Failed to mark party ready"))
+                return@coroutineScope Result.failure(Exception("Failed to mark party ready after 5 attempts"))
             }
 
             // Wait for keygen result