[Enhancement]: Improve DSH startup failure diagnostics

[curryxjh]

Description

Summary

This issue tracks a narrow WP0 diagnostics improvement from #3.

When the DSH E2E Server fails to start, the harness should report enough bounded diagnostic information to make the failure actionable.

Scope

• Make DSH startup failures print the child process exit status when available.
• Include complete bounded Server logs when startup fails.
• Preserve the existing startup timeout behavior.
• Keep this focused on failure diagnostics only.

Acceptance criteria

• A failed DSH startup clearly reports the child exit status if the process has exited.
• Startup failure output includes bounded Server logs.
• Existing DSH E2E behavior remains unchanged except for improved failure diagnostics.