fix: error when legacy is active

[nirbhayel]

✨ PR Description

Purpose: Fix PHP error by preventing remediation and scanner modules from activating when legacy module is active, ensuring mutual exclusivity.

Main changes:

• Added LegacyModule::is_active() checks in remediation and scanner module activation guards
• Imported LegacyModule namespace in both affected module files for compatibility validation
• Modules now return false when legacy mode active, preventing conflicting functionality execution

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