List existing flow rule exceptions on gradebook-single

[Copilot]

• Add flow_rule_exceptions context to view_single_grade in grades.py
• Add deactivate_flow_exception view in views.py (POST-only, requires grant_exception permission)
• Add URL pattern relate-deactivate_flow_exception in urls.py
• Update gradebook-single.html template to show exceptions with summary info, visual styling for inactive ones, and per-rule deactivate buttons
• Add ViewSingleGradeFlowRuleExceptionsTest and DeactivateFlowExceptionTest tests
• Fix test_deactivate_get_not_allowed: pass course_identifier to get_default_instructor_user()

Original prompt

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This section details on the original issue you should resolve

<issue_title>List existing flow rule exceptions on gradebook-single</issue_title>
<issue_description>- The list should show summary information on the exception.

• Also show deactivated rules, but in a visual style that clarifies they're no longer active.
• Also, offer a per-rule button to deactivate currently-active exceptions.</issue_description>

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

• Fixes List existing flow rule exceptions on gradebook-single #1415

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[inducer]

@copilot There's a test failure:

        with self.temporarily_switch_to_user(
>               self.get_default_instructor_user()):
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
E               TypeError: CoursesTestMixinBase.get_default_instructor_user() missing 1 required positional argument: 'course_identifier'

tests/test_grades/test_grades.py:1813: TypeError

Also please consider the AGENTS.md file in the root of the repository.

[Copilot]

@copilot There's a test failure:

        with self.temporarily_switch_to_user(

...

Fixed in 55af831 — get_default_instructor_user() now receives self.get_default_course_identifier() as required.