Add history view for all submissions in assignment group

[Copilot]

Instructors need to view submission history across an entire assignment group, not just individual submissions.

Changes

Backend

• Added /assignment_group/browse_history endpoint in assignment_groups.py
  • Queries all assignments in group and users with logged events
  • Returns comma-separated assignment/user IDs for watcher component
  • Enforces grader-only access

Frontend

• Created templates/assignment_groups/browse_history.html

  • Reuses existing watcher.ts KnockoutJS component
  • Initializes with assignment group's assignments and users
  • Defaults to SUMMARY view mode for at-a-glance overview

• Updated templates/reports/group.html

  • Added "Browse All Submission History" button for graders

Usage

The watcher component already supports multiple assignments/users via the load_history endpoint, so no changes to watcher.ts were needed. The new endpoint simply aggregates the relevant IDs from the assignment group.

/assignment_group/browse_history?assignment_group_id=123&course_id=456

Original prompt

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This section details on the original issue you should resolve

<issue_title>History view across multiple submissions</issue_title>
<issue_description>Currently, there are a few places to view the history of a single submission. I'd like to have a new menu that let's me get the history of all the submissions in a single assignment group and view them the same way. This should be a separate route for the assignment_groups endpoint. You can look at the blockpy endpoint's browse_history function to see how that handles things. You can also check out watcher.ts in the frontend to see how that works and renders. I'd like most of the logic for this to be in the frontend Knockoutjs application side, rather than using the jinja2 template approach. Obviously, the backend controllers and models should handle extracting out the events.</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes History view across multiple submissions #78

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