Admin products: UI/UX improvement plan for plan create/list
Imported from GitHub issue El-SaMa/oma#166 by @El-SaMa.
Operator asked for better admin UX when creating and listing plans/products (free domain endings field was added, rest is open).
Write a plan first and show it to the operator before building: list view (prices, free domain endings, grandfathered counts), create/edit in a modal, vertical side nav (no second tab row), shadow cards. Must stay covered by oma.admin_catalog_product_* tools.