feat(web): notification (and sound) when a thread finish - #7348

💭 Looking at the diff, most changed files are React/UI code rather than Effect services, but the settings contracts file adds schema definitions with decoding defaults, so I want to check whether it imports Effect directly. I don't see any Effect services, Layers, or runPromise usage in this diff—it's just React UI plus a contracts schema addition, and Settings.ts already uses namespace imports consistently. Since there are no findings, I need to reconcile the instruction to respond with exactly "All clear" against the requirement that the final response be valid JSON per the schema. I'll resolve this by setting the state to success with title/summary "All clear" — the check defaults to failure only when findings exist, so no findings means success.