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/plugins/PluginsScreen.kt

@@ -59,10 +59,11 @@ fun PluginsScreen(
     HermesScaffold(
         title = { Text("Plugins") },
         onOpenDrawer = onOpenDrawer,
+        isRefreshing = state.isLoading,
         onRefresh = { viewModel.loadPlugins() },
     ) { paddingValues ->
         when {
-            state.isLoading -> {
+            state.isLoading && state.plugins.isEmpty() -> {
                 LoadingState(modifier = Modifier.padding(paddingValues))
             }
             state.errorMessage != null -> {