feat(#13): add pull-to-refresh to HermesScaffold (#14)

- HermesScaffold: added isRefreshing param, wraps content in PullToRefreshBox when onRefresh is set
- All 16 data screens: pass isRefreshing = state.isLoading
- Initial loading only shows full-screen LoadingState when data is empty (no spinner over existing content)
- AchievementsScreen already had the correct pattern, just needed isRefreshing param

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/ui/cron/CronJobsScreen.kt

@@ -61,10 +61,11 @@ fun CronJobsScreen(
     HermesScaffold(
         title = { Text("Cron Jobs") },
         onOpenDrawer = onOpenDrawer,
+        isRefreshing = state.isLoading,
         onRefresh = { viewModel.loadCronJobs() },
     ) {
         when {
-            state.isLoading -> LoadingState()
+            state.isLoading && state.jobs.isEmpty() -> LoadingState()
             state.errorMessage != null ->
                 ErrorState(
                     message = state.errorMessage ?: "Unknown error",