Quiz Time Limit

[tigerpadla]

As a user, I want some quizzes to have a timer, so that I can challenge myself under time constraints.

Acceptance Criteria

• Timer appears on each question or overall quiz.
• Quiz automatically submits when time is up.
• Score calculation works correctly with time-limited quizzes.

Tasks

• Add optional time_limit field to Quiz model.
• Implement countdown timer in quiz template.
• Handle automatic submission in backend.