fix(store): validate courseProgressStore updates with type guard

[Nacho1499]

Closes #808

Summary:
Implemented runtime validation and narrowing for lessonData updates in courseProgressStore.ts to prevent incomplete or invalid state transitions:

• Added isValidLessonProgress type guard to verify required LessonProgress fields (lessonId, completed, lastPosition, timeSpent, completedAt).
• Created and threw a custom InvalidLessonProgressError whenever incomplete lessonData is supplied before spreading candidate progress into the store.
• Updated tsconfig.json test exclusion boundaries and added unit tests in courseProgressStore.test.ts covering type guard logic, invalid state rejection, and store state immutability on thrown errors.

Type of Change:
[x] Bug fix (non-breaking change which fixes an issue)

Testing Done:
[x] Unit Tests
[x] Manual Verification (e.g., iOS/Android UI checks)

Security Considerations:
[x] Are all user inputs validated?

Checklist:
[x] I have read the CONTRIBUTING guide.
[x] My code follows the style guidelines of this project.
[x] I have updated the documentation accordingly.

[drips-wave]

@Nacho1499 Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits

[RUKAYAT-CODER]

Thank you for contributing to the project.