fix: harden widget query persistence and refresh indicator

Review follow-ups on the session query cache:

- Cache the per-payload size verdict and reuse a single TextEncoder. The
  persist subscription re-dehydrates the whole cache on every cache event,
  so every widget payload was being superjson-serialized several times per
  refresh cycle just to measure it.
- Skip the size measurement on the restore path. It runs before any query is
  allowed to fetch and the payload was already budgeted when it was written.
- Reject stored queries whose dataUpdatedAt is not a positive finite number;
  `undefined <= 0` is false, so those were hydrating with a NaN timestamp.
- Add `stop()` and tear the persister down before `queryClient.clear()`, so
  the clear cannot overwrite the saved snapshot with an empty cache.
- Remove every other scope's cache when a persister is created: signing out
  navigates away before the scope guard can react, which left the previous
  account's dashboard data in the tab.
- Remove the entry instead of storing an empty cache.

Refresh indicator:

- Make it decorative instead of an aria-live region; every widget refreshes
  on a timer, so it made assistive technology repeat "loading" forever.

Also broadens the e2e hydration-error matcher to production React's minified
error codes, hoists the single WidgetTimeProvider in ClientBoard, memoizes the
resolved local time zone, and drops the exports this branch made dead.

apps/nextjs/src/components/board/items/item-content.tsx

@@ -2,7 +2,7 @@ import type { ComponentType, CSSProperties, MutableRefObject, PropsWithChildren
 import { memo, Suspense, use, useCallback, useEffect, useMemo, useRef, useState } from "react";
 import { createPortal } from "react-dom";
 import dynamic from "next/dynamic";
-import { Box, Button, Center, Loader, Portal, VisuallyHidden } from "@mantine/core";
+import { Box, Button, Center, Loader, Portal } from "@mantine/core";
 import { useElementSize, useIsomorphicEffect } from "@mantine/hooks";
 import { QueryErrorResetBoundary, useIsFetching, useQueryClient } from "@tanstack/react-query";
 import combineClasses from "clsx";
@@ -343,10 +343,14 @@ const LoadedBoardItemContent = ({
           />
         </ErrorBoundary>
       </Box>
+      {/*
+        Purely decorative: widgets keep showing their previous data while they
+        refresh, and every widget refreshes on a timer, so announcing this would
+        make assistive technology repeat "loading" for the whole board forever.
+      */}
       {isWidgetRefreshing && (
-        <Box className={itemContentClasses.refreshIndicator} component="output" aria-live="polite">
+        <Box className={itemContentClasses.refreshIndicator} data-widget-refreshing aria-hidden>
           <Loader size="xs" />
-          <VisuallyHidden>{t("common.action.loading")}</VisuallyHidden>
         </Box>
       )}
     </WidgetCardShell>