Restore green CI on main: ruff B905 (zip strict=) from 6db5c2b3 blocks the quality job

[alexeygrigorev]

Observed by on-call after the #382 merge push (d7e53f5, CI run 35010874544) and confirmed pre-existing.

Evidence

• Job quality fails: ruff B905 zip() without explicit strict= at courses/tests/test_course_illustrations.py:127. Reproduced locally at d7e53f5f with the exact CI command. Introduced by 6db5c2b3 (pushed 18:11Z); quality passed at the prior head 55a400c7 (15:56Z).
• Because the quality contract aborts on first failure, django/playwright were cancelled at b297191d and d7e53f5f. Deploy Dev verify-ci failed, deploy skipped.
• Independent pre-existing red: at 55a400c7 (quality green), django failed with failures=16, errors=1 and playwright failed (accessibility/article-parity among them). Attribution of those to introducing commits is still open; do not treat them as acceptable.

Acceptance criteria

• B905 fixed (strict=True; the zipped literals are equal-length) and the full quality contract passes locally, not just to the first failure
• typecheck and format-check targets re-run clean (separate assert is not None narrowing and reflow fixes are in flight in the shared checkout)
• push to main re-observed: quality, django, playwright jobs all green or each remaining failure attributed to an owning issue
• Deploy Dev goes green at the fixed head

Fix is in progress in the shared main checkout (uncommitted at time of filing); commit with Refs #N pointing at this issue.