Refactor StudentAppService method naming for consistency

[coderabbitai]

Context

In IStudentAppService, there's a naming inconsistency between methods:

• GetStudentByEmailAsync (includes 'Student' in the name)
• GetByIdNumberAsync (omits 'Student')

For consistency, GetByIdNumberAsync should be renamed to GetStudentByIdNumberAsync.

Notes

• The email endpoint is stale and will be kept around until the admin dashboard is implemented
• This refactoring should be completed before release
• Note: Please manually add this to the 'Pre release cleanup' milestone

References

• PR: Feature/application First Step E2E #39
• Comment: Feature/application First Step E2E #39 (comment)
• Requested by: @blebelo