Offer Search again only where the photo backfill runs (Maestro 7a468d2d, review F1/F2)

F1: every dinner response now carries photo_backfill_eligible, computed
by the exported dinners.PhotoBackfillEligible: the condition
ListPhotoBackfillDinners lists by and GroundFailedDinner and
RefailDinnerGrounding write under (unarchived, failed, no photo, no
pasted recipe_url). A test holds the flag to ListPhotoBackfillDinners
for an eligible dinner and for grounded, linked and archived ones. The
fix-recipe sheet shows "Search again" only when the flag is set, so a
dinner with a pasted link is never offered it, whatever its reason.

F2: a dinner absent from the backfill result now reads "This dinner was
not included in that search." instead of claiming a pasted link.

Task: 7a468d2d-4a9b-45f2-b626-a7bed5f671df

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

internal/dinners/backfill.go

@@ -25,6 +25,17 @@ const (
 	BackfillSkipped = "skipped"
 )
 
+// PhotoBackfillEligible reports whether a photo backfill grounds r: the
+// condition ListPhotoBackfillDinners lists dinners by, and GroundFailedDinner
+// and RefailDinnerGrounding write under, for one dinner. The dinner is
+// unarchived, failed, with no photo and no pasted recipe_url.
+func PhotoBackfillEligible(r db.Dinner) bool {
+	return r.Status != StatusArchived &&
+		r.GroundingStatus == GroundingFailed &&
+		!r.PhotoID.Valid &&
+		!r.RecipeUrl.Valid
+}
+
 // BackfillJob is the KindBackfillPhotos payload. DinnerID narrows the
 // backfill to that dinner; empty backfills every dinner without a photo.
 type BackfillJob struct {