feat(billing): 完成异步结算与请求执行闭环

统一任务成功、Attempt 与结算 Outbox 的事务边界，增加多实例安全结算、人工复核、请求幂等与执行租约。钱包决策使用九位精确金额，并通过审计保护约束保留流水事实；同时补充管理接口、指标与 PostgreSQL 集成测试。

apps/api/internal/runner/wallet_execute_test.go

@@ -182,6 +182,20 @@ func TestExecuteWithMockClientRejectsConcurrentTasksBeyondWalletBalance(t *testi
 	if got := mockClient.calls.Load(); got != 1 {
 		t.Fatalf("mock client calls = %d, want 1", got)
 	}
+	settlements, err := db.ClaimBillingSettlements(ctx, "wallet-execute-test", store.BillingSettlementBatchSize, store.BillingSettlementLockTimeout)
+	if err != nil {
+		t.Fatalf("claim billing settlements: %v", err)
+	}
+	processed := 0
+	for _, settlement := range settlements {
+		if err := db.ProcessBillingSettlement(ctx, settlement); err != nil {
+			t.Fatalf("process billing settlement %s: %v", settlement.ID, err)
+		}
+		processed++
+	}
+	if processed != 1 {
+		t.Fatalf("processed billing settlements = %d, want 1", processed)
+	}
 
 	summary, err := db.GetWalletSummary(ctx, user, "resource")
 	if err != nil {