Name the dinners.Dinner responses that carry photo_backfill_eligible (F23-1)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/ARCHITECTURE.md

@@ -276,10 +276,12 @@ automatic** (D-021).
   `grounded`, `failed` (with its reason) or `skipped`. A dinner whose write
   fails is `failed` with `grounding_error` and left as it was; the others
   still run, then the job fails with `internal_error`, keeping that result.
-  The list and every response that creates or changes a dinner (not
-  `GET /api/v1/dinners/{id}`) carry `photo_backfill_eligible`, whether the
-  backfill grounds that dinner, computed by the same condition it lists
-  dinners by, so a client offers a search only where one runs.
+  The responses returning a `dinners.Dinner` representation (the list; the
+  create, update, archive, favorite and grounding responses; the idea
+  responses) carry `photo_backfill_eligible`, and
+  `GET /api/v1/dinners/{id}` does not; it says whether the backfill grounds
+  that dinner, computed by the same condition it lists dinners by, so a
+  client offers a search only where one runs.
   `GET /api/v1/dinners/{id}/recipe-candidates`
   searches for the dinner's name and returns `{candidates: [{candidate_id,
   title, site_name, photo_url, minutes}]}`, at most 3, ranked as `Ground`