feat: improve Linux bootable USB stability and user experience

- Enhanced Live USB environment detection and support
- Added troubleshooting guide (TROUBLESHOOTING.md)
- Added installation test script (test-installation.sh)
- Improved error handling in PowerShell scripts
- Better network retry logic for downloads
- Enhanced desktop integration for Live environments
- Added detailed improvements summary (IMPROVEMENTS_SUMMARY.md)
- Updated README with troubleshooting links

Key improvements:
1. Auto-detection of Live USB environment (boot=casper)
2. Additional dependency installation for Live environments
3. Network download retry mechanism (3 attempts)
4. Smart browser opening with fallback instructions
5. Comprehensive installation validation script
6. Detailed fault diagnosis and recovery guide

bootable/README.md

@@ -296,3 +296,8 @@ bootable/
 - **Node.js**: v22.14.0 LTS，npmmirror.com（国内）或 nodejs.org
 - **OpenClaw**: npm latest，安装到 `/opt/u-claw/`
 - **完全独立**: 不引用仓库内 `portable/`、`u-claw-app/`、`website/` 的任何文件
+
+## 详细故障排除
+
+遇到问题请参考详细故障排除指南：
+- [TROUBLESHOOTING.md](TROUBLESHOOTING.md) - 完整的问题排查步骤和解决方案