What's That: render one representative tile per illustration group

[WilfordGrimley]

Summary

When a What's That Card question is about which illustration a card uses, the grouped-tile render (illustrationGroups.map in QuestionFeed.tsx) rendered every candidate in the cluster as its own tile, while the tap handler (selectIllustrationGroup) already submits a single illustrationId for the whole group regardless of which member was tapped. A 4-printing group showed 4 near-identical images for a question with one answer; production data has groups as large as 9.

This renders exactly one representative tile per illustration group. The representative is chosen deterministically: the first group member with an artCropUrl set, falling back to the group's first member when none has one. This reuses a signal the render already applies per-tile (a tile's own image already prefers artCropUrl over the full scan), rather than inventing a new one, and the same input data always picks the same tile.

The submitted vote is unchanged: selectIllustrationGroup still receives the group's shared illustrationId (every member carries the same one), now sourced from the representative candidate instead of whichever member was tapped — the network payload is byte-for-byte identical to before. The group's own membership count (Same illustration - N printings) and data-illustration-id attribute are both untouched, so the cluster is still discoverable.

Separately, this investigated the issue's second symptom ("the first row of illustrations is hidden"). Live-browser reproduction (Playwright against the running app with a mock backend) showed the illustration group rendering clearly and visibly immediately below the "Filter by attribute" toggle, with its label, printing count, artist credit, and representative tile all present — it did not reproduce. No suppression, filter, or hiding logic exists in the render path, consistent with the prior static-code finding; this change does not touch anything that would affect visibility, and the symptom did not appear in this reproduction attempt.

Test plan

• jest src/features/questionFeed/QuestionFeed.test.tsx — all 21 tests pass, including 2 new tests covering the art-crop-preferred representative pick (regardless of the crop's position in the group) and the fallback to the group's first member when no member has a crop
• tsc --noEmit on the changed file — no new type errors (two pre-existing, unrelated errors from a missing generated asset and a dev-only module are present on master too)
• Live-browser check (Playwright, mock backend): a 4-member illustration group renders exactly one tile (the art-crop member, not the first member), the group's "Same illustration - 4 printings" label and artist credit render normally and visibly, the ungrouped candidate renders separately and unaffected, and clicking the representative tile submits { illustrationId: <shared id> } to /2/submitIllustrationVote/ — identical to the pre-existing vote contract