🧪 Add test coverage for sync_curriculum_ui_labels

[dynamikdev]

🎯 What: Added a missing unit test for the sync_curriculum_ui_labels system in src/ui/systems.rs. This system correctly updates text elements with curriculum state properties (grade, doc, and page).

📊 Coverage: Covered the test gaps by asserting that sync_curriculum_ui_labels applies new text correctly to CurriculumGradeButton, CurriculumDocumentButton, and CurriculumPageText elements by inserting a new CurriculumState into a test App.

✨ Result: Improved test coverage within the ui/systems module, validating the state changes correctly reflect in UI output.

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PR created automatically by Jules for task 8263656239469897631 started by @dynamikdev

[google-labs-jules]

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