Product Sales Channels redesigned

We've redesigned the Sales Channels card on the product edit page to replace a flat list of toggles with a status-based grouping system. Channels are now organized into three categories: Live on (where customers can buy), Hidden from (where the product exists but isn't visible), and Needs attention (channels with setup issues like unpublished sites or missing payment plans). Each channel row expands to show its status, shortcuts to view or edit the channel, and a per-channel toggle. The header displays a live count of active channels for quick reference.