feat: replace server-side Redis caching with TanStack Query AsyncStoragePersister

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

packages/api/src/query-cache.ts

@@ -1,7 +1,10 @@
 import type { QueryKey } from "@tanstack/react-query";
 
-export const queryCacheRetentionMs = 1000 * 60 * 60 * 24;
-export const queryCacheDefaultStaleTimeMs = 1000 * 60 * 5;
+// ponytail: staleTime 0 = always refetch on mount (fresh data every dashboard load).
+// refetchInterval 30s = poll while page is open. gcTime 24h = Redis TTL for persisted cache.
+export const queryCacheDefaultStaleTimeMs = 0;
+export const queryCacheDefaultRefetchIntervalMs = 30_000;
+export const queryCacheDefaultGcTimeMs = 1000 * 60 * 60 * 24;
 export const queryCacheMaxValueBytes = 1024 * 1024;
 export const queryCacheStoragePrefix = "homarr-widget-query";