Replace catalog bulk update with partial/replace APIs

[gmethvin]

Replace the bulk catalog update API with two methods that match Iterable's bulk endpoint and the existing single-item PATCH/PUT methods:

• partialUpdateCatalogItems merges uploaded fields (replaceUploadedFieldsOnly: true)
• replaceCatalogItems replaces each item with only the provided fields (replaceUploadedFieldsOnly: false)

Both accept { catalogName, documents } where documents is a map of item ID to arbitrary JSON fields. The client posts directly to POST /api/catalogs/{catalogName}/items with no items array, dataFields flattening, or required name field.

Breaking changes:

• Removed updateCatalogItems, UpdateCatalogItemParamsSchema, CatalogItemSchema, and CatalogItem
• Removed UpdateCatalogItemParams (singular) naming in favor of PartialUpdateCatalogItemsParams / ReplaceCatalogItemsParams