[QTI] Carry legacy hints into generated QTI items as dormant catalog content

[rtibbles]

Overview

Legacy assessment items carry progressively-revealed hints (AssessmentItem.hints) that the QTI generator drops. Emit them into the generated QTI item as a qti-catalog-info catalog of support="kolibri:hint" cards — dormant content the QTI 3.0 schema excludes from default delivery — carried in raw_data through publish so Kolibri can render them. Legacy-only; the new editor does not author hints.

Complexity: Medium
Target branch: unstable

Context

• Legacy hints: AssessmentItem.hints is a JSON list [{"hint": <markdown>, "order": N}]; base.py:_process_hints converts markdown→HTML and extracts images.
• The QTI generator (utils/assessment/qti/) emits nothing for hints today.
• XSD validation ([QTI] QTI 3.0 schema XML validation utilities #6005) is authoritative and runs on save/publish.

The Change

Emit legacy hints into the generated QTI item as a dormant qti-catalog-info catalog — rendered by Kolibri, ignored by default players.

• One qti-card support="kolibri:hint" per hint, in display order; hint HTML inside qti-html-content.
• id="kolibri-hints" — value not load-bearing; Kolibri selects on support.
• Image refs emitted as standard src so the existing file scan ([QTI] Allow API endpoint to handle AssessmentItem.raw_data to store QTI data #5999) claims them.
• No hints → no qti-catalog-info.

<qti-catalog-info>
  <qti-catalog id="kolibri-hints">
    <qti-card support="kolibri:hint"><qti-html-content><p>First hint…</p></qti-html-content></qti-card>
    <qti-card support="kolibri:hint"><qti-html-content><p>…solution.</p></qti-html-content></qti-card>
  </qti-catalog>
</qti-catalog-info>

Acceptance Criteria

• A legacy item with hints generates a qti-catalog-info with one qti-card support="kolibri:hint" per hint, in original order
• Hint markdown is converted to HTML wrapped in qti-html-content
• Hint images resolve as packaged files via the existing file scan ([QTI] Allow API endpoint to handle AssessmentItem.raw_data to store QTI data #5999)
• An item with no hints generates no qti-catalog-info
• Generated items validate against the QTI 3.0 XSD ([QTI] QTI 3.0 schema XML validation utilities #6005)
• Tests cover multi-hint ordering, a hint with an image, and the no-hints case

References

• QTI 3.0 qti-catalog-info (dormant catalog content): https://www.imsglobal.org/spec/qti/v3p0/impl

AI usage

Claude verified the carrier against the QTI 3.0 ASI XSD — confirming qti-catalog-info holds dormant, non-delivered content, accepts a custom kolibri:hint support value, and that HTML <template> is restricted to custom-interaction markup — then drafted the issue section by section. The maintainer chose the catalog approach and the kolibri:hint value and steered each section.