Switch notifications store from state to context

Editor assessment

The subject is technically clear, the notifications store moved from component state to a context, but that is an architecture change offered with no motivation at all: no note on what problem state caused, prop drilling or stale renders, and no description of the new provider contract. Fix is a questionable type for a structural swap where refactor fits better, though the straddle is arguable. No scope, no body, no footers. Hygiene is otherwise fine. Understandable and valid, but the missing why is exactly what would have made it instructive.