fix(service-party-app): 补全 getSessionStatus 返回的 threshold 和 participants

问题：
- Session.tsx 期望 session 对象有 threshold 和 participants 字段
- 但 grpc:getSessionStatus 只返回了基础字段
- 导致前端显示 参与方 (0 / 0)

修复：
- 从 activeKeygenSession 获取 threshold 信息
- 从 API 返回的 participants 构建完整的参与者列表
- 添加 walletName, currentRound, totalRounds 字段

Generated with Claude Code

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

backend/mpc-system/services/service-party-app/electron/main.ts

@@ -859,15 +859,30 @@ function setupIpcHandlers() {
   ipcMain.handle('grpc:getSessionStatus', async (_event, { sessionId }) => {
     try {
       const result = await accountClient?.getSessionStatus(sessionId);
+      // 从 activeKeygenSession 获取更完整的信息
+      const threshold = activeKeygenSession?.threshold || { t: 0, n: result?.total_parties || 0 };
+      const participants = result?.participants?.map((p, idx) => ({
+        partyId: p.party_id,
+        partyIndex: p.party_index,
+        name: activeKeygenSession?.participants?.find(ap => ap.partyId === p.party_id)?.name || `参与方 ${idx + 1}`,
+        status: p.status,
+        joinedAt: new Date().toISOString(),
+      })) || [];
+
       return {
         success: true,
         session: {
           sessionId: result?.session_id,
+          walletName: activeKeygenSession?.walletName || '',
           status: result?.status,
           completedParties: result?.completed_parties,
           totalParties: result?.total_parties,
           sessionType: result?.session_type,
           publicKey: result?.public_key,
+          threshold: threshold,
+          participants: participants,
+          currentRound: 0,
+          totalRounds: 4,
         },
       };
     } catch (error) {