Add Multiple Products Directly in the UI

Adding a handful of new products no longer requires a bulk spreadsheet import. Multiple products can now be created at the same time directly in Endless, starting with just the essentials like product name and SKU.

This fits the broader Endless approach to catalog building: start simple, then enrich each product incrementally rather than trying to get everything perfect in one giant import. For small batches, it is a much faster way to get items into the system and keep moving.