🧪 test: improve error testing for registerLoginItem

[hatimhtm]

🎯 What: The testing gap in registerLoginItem method inside AppDelegate.swift which previously called SMAppService directly. While testing this behavior, errors could not easily be triggered since the interaction was hard-coded against the system environment.
📊 Coverage: Refactored registerLoginItem using dependency injection (loginItemRegistrationHandler) and a new lastLoginItemError property to capture any potential throwing errors for inspection in tests.
✨ Result: Now includes AppDelegateTests.swift mapped in Click2MinimizeTests target to cover successful login item registration and explicitly check error throwing flows without relying on actual system environmental constraints. Included project.pbxproj and Click2Hide.xcscheme modifications properly utilizing XCTest.framework dependencies and correct .plist setup.

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PR created automatically by Jules for task 8562062387852003197 started by @hatimhtm

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