Show “Shared question” label in lesson quiz question lists + add “Shared” column to Questions list

[amroland]

Description
Currently when an existing question is added to multiple quizzes, it becomes a shared entity. This feature works well. However, it is very difficult to identify which questions are shared across multiple quizzes.
At the moment, a question is only labeled as a “Shared question” when you edit the given lesson, scroll to the quiz, and clicks into a question. The indicator appears inside the question editor.
This means that identifying shared questions requires opening lessons one by one and clicking into each question individually — which is time-consuming and inefficient.
It would greatly improve usability if shared questions were visibly marked in question lists, without requiring extra clicks.

Steps to Reproduce

1. Create two quizzes.
2. Add the same existing question to both quizzes (creating a shared question).
3. Open a quiz and view the question list.
4. Observe that there is no visible label showing that the question is shared.
5. Click into the question itself — only then does the “Shared question” indicator appear.

Expected behavior

• When viewing a quiz’s question list, any question that is shared should display a visible label like “Shared question”, without needing to click into the question.
• In the global Sensei LMS → Questions list, there should be an additional column (e.g., “Shared” or “Used in multiple quizzes”) that indicates whether each question is shared.

Actual behavior

• The system only shows the "Shared question" indicator inside the single question editor.
• The quiz question list and the global Questions list provide no information about whether a question is shared.

Why this improvement is useful

• Makes it much easier for instructors to understand which questions are linked across quizzes.
• Reduces the risk of unintentionally modifying a question that affects multiple quizzes.
• Improves workflow for large sites with many quizzes and shared questions.