feat: Add PUT and PATCH datasets endpoints

internal/repository/postgres/dataset.go

@@ -68,6 +68,23 @@ func (r *DatasetRepository) Create(ctx context.Context, d domain.Dataset) (domai
 	return out, mapError(err)
 }
 
+// UpdateFields overwrites a dataset's editable metadata columns (category,
+// name, description, unit). description and unit are nullable: a nil pointer
+// clears the column. Returns domain.ErrNotFound if the dataset does not
+// exist, or domain.ErrConflict if categoryID does not reference an existing
+// category.
+func (r *DatasetRepository) UpdateFields(ctx context.Context, id, categoryID uuid.UUID, name string, description, unit *string) (domain.Dataset, error) {
+	row := r.pool.QueryRow(ctx,
+		`UPDATE datasets
+		 SET category_id = $2, name = $3, description = $4, unit = $5, updated_at = now()
+		 WHERE id = $1
+		 RETURNING `+datasetColumns,
+		id, categoryID, name, description, unit,
+	)
+	out, err := scanDataset(row)
+	return out, mapError(err)
+}
+
 // MarkParsed stores the detected attribute columns and moves the dataset to
 // awaiting_mapping, clearing any previous parse error.
 func (r *DatasetRepository) MarkParsed(ctx context.Context, id uuid.UUID, cols []domain.AttributeColumn) error {