Add ICommandRunner for safe cross-platform process execution

[JusterZhu]

Summary

Add a process execution abstraction to eliminate direct Process.Start calls and their associated command injection risks.

Changes

• ICommandRunner: interface for cross-platform command execution with argument list support
• CommandRunner: safe Process wrapper using ArgumentList (no shell parsing, no injection risk)
• CommandResult: structured result with exit code, stdout, stderr
• Migrate WindowsGeneralDrivelution PnPUtil calls to use ICommandRunner
• Migrate LinuxGeneralDrivelution insmod/modprobe/dpkg/rpm calls to use ICommandRunner
• Constructor injection: both Windows and Linux updaters accept ICommandRunner

Why

Current code concatenates arguments as strings which is vulnerable to path injection. The new approach passes each argument separately via ProcessStartInfo.ArgumentList.

Closes #288