Changes

Add guideline on understanding code before committing

Added guideline about understanding and explaining code before committing.

Clarify variable usage in coding guidelines

Added guideline to avoid using two variables for the same purpose.

Introduce `XapiStatementExt.kt` to centralize xAPI helper functions and refactor student grouping ViewModels.

Remove unused `SchoolDataSource` import in `XapiStatementExt.kt`.

Update AGENTS.md to refer to CODING_GUIDELINES.md

Implement initial version of getAssignmentProgress

Add xapiAgent property to RespectSessionAndPerson

Add Uuid opt-in to respect-app-compose and respect-lib-shared.

Remove unused `SchoolDataSource` import in `XapiStatementExt.kt`.

Add studentsXapiGroup function

Update group filtering logic in `ClazzDetailViewModel.kt` to handle null timestamps and ensure distinct groups are correctly mapped from xAPI statements.

Remove `XapiStatementExt.kt` and inline xAPI agent and statement creation logic within `StudentGroupingDetailViewModel` and `StudentGroupingEditViewModel`. Use `xapiAgent` directly from the selected account session and manually construct `XapiStatement` and `XapiAgent` objects for group management and voiding operations.

Remove unnecessary empty lines in `ClazzDetailViewModel.kt`.

Apply minor formatting and whitespace adjustments to `ClazzDetailViewModel.kt`.

Improve error handling and data robustness in student grouping view models and screens.

- Add `Napier` logging and replace potential crashes with safe checks and early returns in `StudentGroupingDetailViewModel`, `ClazzDetailViewModel`, and `StudentGroupingEditViewModel`.
- Refactor `StudentGroupingEditState` to calculate `selectedStudentIds` dynamically from the student list.
- Enhance group filtering and mapping logic in `ClazzDetailViewModel` to handle missing group/member data gracefully.
- Update UI components in `StudentGroupingEditScreen` and `ClazzDetailScreen` to safely handle null items and improve key mapping.
- Delete unused `XapiActorDataSource.kt`.