[IMPROVEMENT] Verify native Windows shell-run compatibility end to end

Current state

Windows x64 is a supported OpenSRE release target, but Windows CI is optional and the native shell_run path does not yet have a real end-to-end compatibility scenario. PR #6215 adds deterministic cmd.exe execution, Windows-aware policy checks, portable pwd, and process-tree cleanup while fixing the Linux report in #6206.

Desired state

Verify native Windows behavior through the real uv run opensre ask --allowed-tool shell_run ... path and document the supported shell contract. The verification should cover compact operators, quoting/escaping, environment expansion, working-directory isolation, output, timeout, and descendant cancellation.

Success means the focused native-Windows scenario and the optional Windows quality/full-test workflow pass, and user-facing docs clearly distinguish native cmd.exe behavior from WSL/POSIX behavior.