Report the latest failed suggestion batch on the deck

The deck reported only a pending or running batch, so a Discover page
opened after a batch failed (or was interrupted by a restart) had no job
to follow and showed "All caught up" or the remaining cards with no
error. GET /api/v1/suggestions/deck now also returns failed_batch: the
newest batch when it failed, read in the same snapshot after orphaned
batches are failed, so at most one of active_batch and failed_batch is
set and a later batch supersedes the failure. The page follows the
failed batch's job like the active one, so its failure shows with the
existing Retry, which asks for a new batch.

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

internal/db/suggestions.sql.go

@@ -187,6 +187,28 @@ func (q *Queries) GetActiveSuggestionBatch(ctx context.Context) (SuggestionBatch
 	return i, err
 }
 
+const getLatestSuggestionBatch = `-- name: GetLatestSuggestionBatch :one
+SELECT id, "trigger", status, ai_run_id, created_at, updated_at FROM suggestion_batches
+ORDER BY id DESC
+LIMIT 1
+`
+
+// The newest batch, whatever its status. Returns sql.ErrNoRows when there
+// is none.
+func (q *Queries) GetLatestSuggestionBatch(ctx context.Context) (SuggestionBatch, error) {
+	row := q.db.QueryRowContext(ctx, getLatestSuggestionBatch)
+	var i SuggestionBatch
+	err := row.Scan(
+		&i.ID,
+		&i.Trigger,
+		&i.Status,
+		&i.AiRunID,
+		&i.CreatedAt,
+		&i.UpdatedAt,
+	)
+	return i, err
+}
+
 const getSuggestion = `-- name: GetSuggestion :one
 SELECT suggestions.id, suggestions.dinner_id, suggestions.batch_id, suggestions.name, suggestions.reason, suggestions.cited_regular_ids, suggestions.status, suggestions.decided_at, suggestions.created_at, suggestions.updated_at, dinners.id, dinners.name, dinners.normalized_name, dinners.status, dinners.origin, dinners.method, dinners.minutes_total, dinners.difficulty, dinners.cuisine, dinners.is_favorite, dinners.recipe_id, dinners.photo_id, dinners.grounding_status, dinners.updated_by, dinners.created_at, dinners.updated_at, dinners.recipe_url, dinners.grounding_error, dinners.grounding_revision
 FROM suggestions