fix(marketplace): track adoptions through a course roll-forward

[adi-herwana-nus]

Adoption rows were keyed off the SOURCE's own marketplace listing, so they only ever fired for copies of the authoring assessment. A copy of an adopted copy -- next semester's course, rolled forward -- carries no listing of its own, so it dropped out of the listing's reach silently: no adoption row, no "a newer version is available" reminder ever again, and the count missed a course genuinely using the content.

Key the row off the source's own adoption row instead. The chain now propagates through every generation, and each copy inherits the vintage its source holds rather than what the listing currently serves, so a rolled-forward copy is still told when it falls behind.

Copies of the assessment that AUTHORS a listing stop being recorded. Those are the publisher's own -- their course rolled forward, or the assessment handed to a colleague directly -- made without anyone choosing the listing, and recording them let a listing with no adopters at all show an adoption count that climbed every semester its author re-ran the course.

[Copilot]

Pull request overview

This PR fixes marketplace adoption tracking so that adoption records and version-reminder reach propagate through “roll-forward” generations (copy of an adopted copy), while excluding duplicates of the publisher’s own authoring assessment that did not come through a marketplace adoption.

Changes:

• Update Course::Assessment#record_marketplace_adoption to key propagation off the source assessment’s existing adoption row (preserving the adopted vintage), rather than the source’s marketplace listing.
• Add model-level specs covering: no-op for listing authoring copies, propagation from adopted copies, vintage inheritance, unlisted listings, and preview container exclusion.
• Update duplication job specs to reflect the new distinction between duplicating the listing’s authoring assessment vs duplicating an adopted copy (roll-forward propagation).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
spec/models/course/assessment_spec.rb	Adds focused coverage for adoption propagation semantics and edge cases.
spec/jobs/course/assessment/marketplace/duplication_job_spec.rb	Adjusts expectations for manual duplication to distinguish authoring copies vs adopted-copy roll-forward.
app/services/course/duplication/base_service.rb	Updates inline documentation to reflect adoption propagation intent for duplication paths outside the marketplace job.
app/models/course/assessment.rb	Implements propagation via the source adoption row and preserves the source’s adopted vintage timestamp.

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