stop, disable and remove modemmanager service

[brabster]

fixes #41
fixes #43

[Copilot]

Pull Request Overview

This PR implements the removal of ModemManager service and package to comply with UK Cyber Essentials requirements by reducing attack surface and eliminating unnecessary services.

Key Changes:

• Adds systemd task to disable and stop ModemManager service
• Adds package removal task for modemmanager package
• Updates task description to clarify scope of package removal

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
roles/cleanup/tasks/main.yml	Adds ModemManager service disabling and package removal tasks with compliance annotations
CHANGELOG.md	Documents the security enhancement with threat model assessment and compliance rationale

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