prices stored as float64 could lead to rounding errors when converting to cents for stripe (19.99 * 100 = 1998.99... truncating to 1998). canged Coffee.Price to int, storing cents directly. Updated the seed data, fallback products, API handlers, and all TUI display code to be in sync with this change.
replaced ViewingCart/ViewingAccount booleans and CheckoutStep int with a
single 'page' type and a SwitchPage() method, this is just almost
copying the reference implementation (terminalDotShop)'s routing
pattern. Adds inCartFlow(), chechoutStep(), and buildPageContent()
helpers to clean up those huge if/else chains in views, footer, header,
and breadcrumds. code is looking a lot better now!
