Slai Agent Runtime: Fix Windows command capture and runtime paths

[Slai.life (huong8373tt-beep)]

Summary

This PR is limited to Windows command capture and Windows container path handling:

• execute commands through non-interactive Docker exec_run rather than the persistent ConPTY transcript path;
• capture and parse command exit metadata, working directory, and output;
• make the Windows checkout directory explicit (C:\testbed) for each command;
• use native Windows paths for transported patch files;
• preserve UTF-8/UTF-16 output decoding required for Windows evaluator capture.

It keeps the existing runtime API and does not modify task solution patches or evaluator scoring.

Scope intentionally excluded

• Command-deadline / timeout-container cleanup is handled separately by Slai Agent Runtime: Enforce Windows command deadlines #47 for the existing runtime path.
• Recovery when a Docker container disappears while a non-interactive exec_run is blocked is a follow-up that depends on this command-capture implementation; it is not included in this PR.
• Windows proxy policy and Linux runtime changes are outside this PR.

Relationship to nearby PRs

• Slai Agent Runtime: Tolerate Windows patch whitespace drift #46: whitespace-only Windows patch-application tolerance.
• Slai Agent Runtime: Enforce Windows command deadlines #47: timeout cleanup for the existing Windows command path.
• Slai Agent Runtime：Normalize Linux evaluator patch files on Windows hosts #57: Linux evaluator patch byte normalization.
• Slai Agent Runtime：Use POSIX paths for Linux mounted patches #58: POSIX patch paths for Linux containers.

Validation

The change was prepared from Windows evaluation replays that exposed incomplete ConPTY captures and invalid Windows patch paths. This PR is intentionally scoped to command capture and runtime path behavior; it does not claim the separate timeout/liveness follow-up as part of its diff.

Prepared by Slai Agent Runtime through the Slai.life GitHub account.