- Add double join on translations for source/target languages
- Left join term_glosses for optional source-language glosses
- Filter difficulty on target side only (intentionally asymmetric:
a word's difficulty can differ between languages, and what matters
is the difficulty of the word being learned)
- Return neutral field names (sourceText, targetText, sourceGloss)
instead of quiz semantics; service layer maps to prompt/answer
- Tighten term_glosses unique constraint to (term_id, language_code)
to prevent the left join from multiplying question rows
- Add TODO for ORDER BY RANDOM() scaling post-MVP
