Consolidate two overlapping cache systems (broken TanStack persister + per-query Redis hash + pub/sub) into one: TanStack Query as single source of truth with Redis as its persistence layer via createAsyncStoragePersister.
- Replace QueryClientProvider with PersistQueryClientProvider backed by Redis
- Set global query defaults (staleTime: 0, refetchInterval: 30s, gcTime: 24h)
- Remove all per-widget staleTime/refetchInterval/retry/refetchOnWindowFocus overrides
- Replace cached request handlers with simplified fetch-only versions
- Remove all tRPC subscription procedures and useSubscription calls in favor of polling
- Delete 20 cron jobs that only pre-warmed server-side cache
- Simplify Redis from per-query hash to single blob per user+board