Implement catalog startup diagnostics (T-616)

app-modern/ui/gio/shell.go

@@ -34,6 +34,7 @@ type AppShell struct {
 	iconRequests     map[string]application.IconEventIdentity
 	iconApplied      map[string]application.IconEventIdentity
 	iconFailures     map[string]iconFailureState
+	catalogState     catalogPresentationState
 	lastRendered     int
 	detailRendered   bool
 }
@@ -58,6 +59,9 @@ func NewAppShell(
 	}
 	shell.search.SingleLine = true
 	shell.SetItems(items)
+	if len(items) == 0 {
+		shell.catalogState = catalogStateLoading
+	}
 	return shell
 }
 
@@ -76,6 +80,7 @@ func (shell *AppShell) ApplyIcon(appID string, icon image.Image) {
 // SetItems applies a prepared, IO-free catalog/status snapshot.
 func (shell *AppShell) SetItems(items []application.CatalogListItem) {
 	shell.model.SetItems(items)
+	shell.catalogState = catalogStateReady
 
 	nextRows := make(map[string]*rowControls, len(items))
 	nextIcons := make(map[string]paint.ImageOp, len(items))