fix(viewer): re-transform quiz questions on restart and default isAssessment to true

[vpPavithra]

Summary

• On "Yes, Restart", the quiz overview flow now re-fetches and re-transforms the quiz artifact JSON (transformQuiz) before reopening the assessment/quiz dialog, so restarted attempts use freshly derived questions/question types instead of stale in-memory ones.
• assessment-detail.component.ts: default quizJSON.isAssessment to true when the content doesn't explicitly specify it (was defaulting to false).

Tests

• Added quiz.component.spec.ts covering transformQuiz (URL derivation, questionType defaulting, error handling) and the restart flow in openOverviewDialog.
• Added assessment-detail.component.spec.ts covering the isAssessment default behavior and ngOnInit.
• Note: specs under project/ are currently excluded by testPathIgnorePatterns in jest.config.js (pre-existing, marked "TEMPORARY: library and project folders blocked — src only"), so these do not run under yarn test yet. Verified logic manually against a modified local jest config; left the config untouched per existing convention.