fix(windows): ensure silent execution and bypass execution policy for subprocesses

[feision]

Problem
On Windows, the agent frequently triggers intrusive CMD/PowerShell console windows when executing scripts (especially via node, npm, or other toolchains). This creates a "flickering" effect that disrupts the user's focus. Additionally, default PowerShell execution policies can sometimes block or stall script execution.

Solution
This PR implements two low-level fixes to ensure a 100% silent and stable background execution environment on Windows:

PowerShell Policy Bypass (ga.py): Added -ExecutionPolicy Bypass to the PowerShell command builder. This prevents execution stalls caused by restricted system policies.

Global Subprocess Suppression (assets/code_run_header.py): Enhanced the subprocess monkey-patch to inject CREATE_NO_WINDOW (0x08000000) into the subprocess.run method. While the existing patch covered Popen, many modern Node.js wrappers use the run interface, which previously bypassed the silent flag.

Impact
Zero Popups: Completely eliminates CMD window flashing during npm install or other long-running tasks.
Stability: Prevents "zombie" or stalled processes due to PowerShell permission prompts.
Transparency: No changes to Linux/macOS behavior.

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问题背景
在 Windows 环境下使用时，GA 运行脚本（尤其是通过 node、npm 或其他工具链）会频繁弹出 CMD/PowerShell 黑色窗口。这种“闪烁”效果非常干扰用户焦点，甚至会导致当前窗口失去焦点。此外，Windows 默认的 PowerShell 执行策略有时会拦截脚本运行，导致执行卡顿或失败。

解决方案
本 PR 针对底层执行逻辑进行了两项关键修复，确保 Windows 下 100% 后台静默且稳定运行：

绕过 PowerShell 执行策略 (ga.py): 在 PowerShell 命令构造中添加了 -ExecutionPolicy Bypass 参数。这解决了因系统权限策略导致的脚本拦截和执行停滞问题。

强制全局静默标志 (assets/code_run_header.py): 增强了 subprocess 的猴子补丁（Monkey Patch），将 CREATE_NO_WINDOW (0x08000000) 标志注入到 subprocess.run 方法中。 原因：原有的补丁仅覆盖了 Popen，但许多现代 Node.js 包装器使用的是 run 接口，这会导致之前的静默标志失效。本次更新确保了所有 Python 派生的子进程均无窗口运行。

改动影响
零弹窗：彻底消除了 npm install 或长耗时任务期间的 CMD 窗口闪烁。
稳定性提升：防止了因 PowerShell 权限提示导致的“僵尸进程”或任务挂起。
无副作用：仅针对 Windows 环境 (os.name == 'nt') 生效，不影响 Linux/macOS 用户。