added cache for dashboard and storage pages

cmd/telesrv-admin/web/src/lib/cache.ts

@@ -0,0 +1,35 @@
+// Last-known values for screens that are visited repeatedly.
+//
+// Navigating back to the dashboard used to re-mount it with empty state, so an
+// operator watched the same numbers redraw from skeletons every time. The
+// screens already refresh themselves; what they lacked was something to show
+// while that happens. Reading from here on mount means the page opens on the
+// figures it had, and the refresh quietly replaces them.
+//
+// Kept in module memory rather than localStorage on purpose. This is admin data
+// -- account counts, storage figures -- and it has no business outliving the
+// tab or sitting on disk. It dies on reload, and clearAdminCache() drops it at
+// sign-out so the next operator in the same tab never sees the previous one's
+// figures.
+
+const store = new Map<string, unknown>();
+
+export function cacheGet<T>(key: string): T | undefined {
+  return store.get(key) as T | undefined;
+}
+
+export function cacheSet<T>(key: string, value: T): void {
+  store.set(key, value);
+}
+
+export function clearAdminCache(): void {
+  store.clear();
+}
+
+// Keys live here rather than as loose strings at each call site, so a typo
+// cannot quietly create a second cache that never hits.
+export const cacheKeys = {
+  dashboard: "dashboard",
+  storageStats: "storage.stats",
+  storageAccounts: "storage.accounts"
+} as const;