Allure Dashboard overview shows incorrect testcase count with Pabot Robot Framework runs

### Describe the Bug

When running Robot Framework tests for multiple websites in parallel using Pabot (with argument files), the Allure Dashboard overview displays only the testcase count for a single URL instead of the total count across all URLs. For example, with 11 testcases per URL and 2 URLs, the timeline correctly shows 22 testcases, but the overview only shows 11.

### Steps to Reproduce

1. Run Robot Framework tests in parallel using Pabot with argument files for multiple URLs:
pabot --listener "allure_robotframework;allure-results" --argumentfile1 arg1.txt --argumentfile2 arg2.txt tests/Global
2. Open the generated Allure report.
3. Observe the timeline tab: it shows the correct total testcase count (e.g., 22).
4. Observe the overview tab: it only shows the testcase count for a single URL (e.g., 11), not the total.

### Expected Behaviour

- The Dashboard overview should display the total number of executed testcases from all parallel runs (i.e., sum across all URLs/sites), matching the count shown in the timeline.
- The pass/fail count should display the total number (sum of pass/fail across all URLs).

### Screenshots or Additional Context

Allure Dashboard - Overview Tab showing only 11 testcase of single url

Allure Dashboard - Timeline Tab showing total 22 testcase of two urls

Environment:
- Allure Commandline version: 2.34.1
- Allure RobotFramework listener version: 2.15.0
- Robot Framework version: 6.1.1
- Pabot version: 4.1.1
- OS: Windows
- Browser: Chrome
- Java version: 24.0.2

### What Language are you using?

Python (RobotFramework)

### What Framework/Allure Integration you are using?

allure-robotframework

### What version of Allure Integration you are using?

2.15.0

### What version of Allure Report you are using?

2.34.1

### Code of Conduct

- [x] I agree to follow this project's Code of Conduct

首先，使用两个参数文件复现报告中的 Pabot 命令，并检查生成的 Allure 报告中的 overview 和 timeline 数据。跟踪并行运行中的 allure-robotframework 结果是如何聚合的；当所有 URL 的 overview testcase 数量及 pass/fail 总数与 timeline 总数一致时，即视为完成。

由索引模型根据 Issue 内容生成。