Each product's description is now built as "Name (цена за M.)" using its
own measure_name. The global description_postfix setting is removed —
it couldn't handle per-product units.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Adds price_multiplier and description_postfix to SyncConfig. The sync
page at /sync lets users configure them. vk_sync reads these per-user
settings and applies the multiplier to price and appends the postfix
as "(postfix)" to the VK product description.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>