Add native Windows compatibility for base-cli testing and terminal behavior

[codeforester]

Parent: #35

Goal

Make the generic test helpers and terminal-facing behavior reliable on Windows 10/11.

Scope

• Make base_cli.testing.invoke(home=...) isolate the relevant Windows home/data environment as well as HOME.
• Preserve process-wide CWD restoration and path handling on Windows.
• Exercise Click invocation through cmd.exe and PowerShell-compatible environments.
• Validate console encoding, newline handling, color detection, and NO_COLOR/explicit color controls.
• Record the effective Windows shell consistently, using COMSPEC when SHELL is absent.
• Keep shell startup files and consumer-specific command execution out of the generic package.

Dependencies

• Requires the platform path contract from Add platform-aware cache paths and home/path normalization #36.
• Requires the privacy/locking behavior from Make private runtime files and history locking portable across POSIX and Windows #37 where tests need runtime files.

Acceptance criteria

• The complete base-cli test suite passes on windows-latest.
• Test helpers do not leak temporary home, cache, or CWD state.
• Terminal output remains deterministic when redirected.