refactor: move system health procedure from system to admin router

- Rename `system.health` → `admin.systemHealth` and gate it behind the admin middleware
- Remove `tmdbConfigured` from `system.status` response; update description to reflect its purpose
- Update all call sites on web and native to use `orpc.admin.systemHealth`
- Rename and relocate the docs page from `system/system.health.mdx` to `admin/admin.systemHealth.mdx`

apps/web/src/components/settings/danger-section.tsx

@@ -29,7 +29,7 @@ export function CacheSection() {
   const queryClient = useQueryClient();
 
   const invalidateHealth = () =>
-    queryClient.invalidateQueries({ queryKey: orpc.system.health.key() });
+    queryClient.invalidateQueries({ queryKey: orpc.admin.systemHealth.key() });
 
   const purgeMetadata = useMutation(
     orpc.admin.purgeMetadataCache.mutationOptions({

apps/web/src/components/settings/system-health-section.tsx

@@ -130,11 +130,11 @@ function LiveTimeAgo({
 export function SystemHealthCards() {
   const queryClient = useQueryClient();
   const { data, isPending, isFetching } = useQuery(
-    orpc.system.health.queryOptions(),
+    orpc.admin.systemHealth.queryOptions(),
   );
   const isRefreshing = isFetching;
   const refresh = () =>
-    queryClient.invalidateQueries({ queryKey: orpc.system.health.key() });
+    queryClient.invalidateQueries({ queryKey: orpc.admin.systemHealth.key() });
 
   if (isPending || !data) return <SkeletonCards />;