Fixes the rest of #70 - mara's answer: "when there are already drinks
in cart, i want to be able to remove them - so show negative numbers
there too."
Second row of -1..-5 buttons appears in the count picker only when the
long-pressed drink already has cart quantity (an empty-cart drink keeps
the original add-only picker - nothing to remove). Routed through
incLine (the qty-stepper's own clamp-at-zero-and-drop-the-line logic)
rather than addDrink's raw qty+n, so over-removing (e.g. -5 on a qty-3
line) drops the line cleanly instead of going negative - verified this
specific clamping behavior with a standalone reproduction of the logic
before trusting it. Remove buttons get the existing button.danger
styling (red), matching the app's established negative/removal
convention (Pfand-return tile, cart-line.return).
pnpm --filter client typecheck and build both clean.
3c9fd3d55c