Rubric Grading: minor fixes, add course-wide grading prompt

[adi-herwana-nus]

Summary

Adds a course-wide grading prompt that course staff can set once, in the assessment settings page,
and have prepended to every rubric-graded question's own grading prompt during AI grading. Alongside
it, this branch fixes a duplication gap for rubric-graded forum questions and removes a piece of dead
v1 rubric-selection machinery from the answer-creation path.

1. Course-wide grading prompt

What it does

When enabled and non-blank, the course prompt is inserted before a question's own grading prompt
whenever a rubric-graded answer is autograded by AI. It gives staff a single place to express grading
guidance that should apply across the whole course, without editing each question.

Storage

Two settings on the assessments component (no migration — these live in the course settings hash,
like show_stdout_and_stderr and programming_max_time_limit):

Accessor	Purpose
Course#rubric_grading_prompt	The prompt text. Setter stores .presence, so blanks are never persisted.
Course#rubric_grading_prompt_enabled	Whether the prompt is applied. Independent of the text, so toggling off preserves it for later.

Injection point

Course::Rubric::RubricAdapter#grading_prompt prepends the course prompt (when enabled and present)
before the rubric's own grading prompt, joined by a blank line; either side may be empty. Because every
grading path — real auto-grading, the apply-evaluations job, and the rubric playground / mock
evaluations — resolves its prompt through this one adapter, the course prompt applies uniformly and the
playground behaves exactly like real grading.

[Copilot]

Pull request overview

This PR extends the rubric AI grading pipeline to support a course-wide grading prompt (configured in Assessment Settings) that is prepended to each rubric question’s prompt when enabled, while also addressing a couple of rubric-related duplication edge cases and cleaning up deprecated v1 rubric-selection scaffolding.

Changes:

• Add course settings (API + UI + i18n) for enabling and editing a course-wide rubric AI grading prompt, and prepend it in Course::Rubric::RubricAdapter#grading_prompt.
• Fix duplication behavior for (a) sibling-answer grading context sources that can be text-response questions, and (b) forum-post questions’ active_rubric so duplicates don’t share the source rubric.
• Remove deprecated v1 rubric-selection factory/initializer paths and update specs accordingly.

Reviewed changes

Copilot reviewed 22 out of 22 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
spec/models/course/rubric/rubric_adapter_spec.rb	Adds specs covering course-wide prompt composition behavior.
spec/models/course/assessment/question/grading_context_spec.rb	Expands duplication coverage for sibling context sources (forum + text response).
spec/models/course/assessment/question/forum_post_response_spec.rb	Ensures duplicated forum questions get a duplicated active_rubric.
spec/factories/course_assessment_answer_rubric_based_response.rb	Removes unused v1 with_selections trait from factory.
spec/factories/course_assessment_answer_rubric_based_response_selection.rb	Deletes deprecated selection factory.
spec/controllers/course/admin/assessment_settings_controller_spec.rb	Adds controller spec ensuring course-wide prompt settings persist.
client/locales/en.json	Adds UI strings for rubric grading settings.
client/locales/ko.json	Adds UI strings for rubric grading settings (Korean).
client/locales/zh.json	Adds UI strings for rubric grading settings (Chinese).
client/app/types/course/admin/assessments.ts	Extends assessment settings types for prompt enable flag + prompt text.
client/app/bundles/course/admin/pages/AssessmentSettings/translations.ts	Adds message descriptors for new rubric grading settings UI.
client/app/bundles/course/admin/pages/AssessmentSettings/operations.ts	Sends new prompt settings fields in update payload.
client/app/bundles/course/admin/pages/AssessmentSettings/AssessmentSettingsForm.tsx	Adds form controls (checkbox + multiline prompt field) and validation.
app/views/course/admin/assessment_settings/edit.json.jbuilder	Exposes new settings in assessment settings JSON payload.
app/models/course/rubric/rubric_adapter.rb	Prepends optional course-wide prompt to rubric prompt when enabled.
app/models/course/assessment/question/text_response.rb	Ensures duplicated text responses participate in grading-context fix-up as sibling sources.
app/models/course/assessment/question/forum_post_response.rb	Duplicates active_rubric during question duplication to avoid sharing rubrics.
app/models/course/assessment/question.rb	Updates documentation for grading-context duplication responsibilities.
app/models/course/assessment/answer/rubric_based_response.rb	Removes v1 selection creation path; keeps deprecated association with clarification.
app/models/course.rb	Adds getters/setters for course-wide rubric grading prompt and enable flag in settings store.
app/models/concerns/course/assessment/submission/answers_concern.rb	Removes v1 selection initialization during bulk answer creation.
app/controllers/course/admin/assessment_settings_controller.rb	Permits new course settings parameters for rubric grading prompt.

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