At most one toast/notification library

Two toast libraries produce two stacking contexts, two animation timings, and two position anchors. A success toast from sonner might render top-right while an error toast from react-hot-toast renders bottom-center, making notifications feel accidental rather than intentional. Users lose trust in the feedback system, and accessibility is also inconsistent: one library might set role="status" while the other uses role="alert", changing how screen readers announce messages.

Pick one and migrate every call. Inventory usage with grep -rl "react-hot-toast" src/, rewrite each call to the survivor's API (both have roughly equivalent toast.success/toast.error shapes), then remove the loser:

npm uninstall react-hot-toast

Centralize toast configuration in src/components/providers/toast-provider.tsx so position, duration, and theming live in one file and future contributors can't accidentally reintroduce a second library.