fix(tests): initialize ProcessingIssuesHandler in test server setup

The setupTestServer() helper in test_helpers_test.go was not creating
a ProcessingIssuesHandler and not passing one to the router config,
causing a nil pointer dereference when any processing issues route was
hit during tests. Add handler creation and wire it into routerConfig
to match how cmd/server/main.go does it.

cmd/server/tests/test_helpers_test.go

@@ -463,6 +463,7 @@ func setupTestServer(t *testing.T) *TestServerSetup {
 	analyticsHandler := handlers.NewAnalyticsHandler(queries)
 	queueHandler := handlers.NewQueueHandler(queries, queueProcessor)
 	systemSettingsHandler := handlers.NewSystemSettingsHandler(queries)
+	processingIssuesHandler := handlers.NewProcessingIssuesHandler(queries)
 
 	// Create refactored handlers (matching main.go)
 	libraryService := services.NewLibraryService(queries)
@@ -518,6 +519,7 @@ func setupTestServer(t *testing.T) *TestServerSetup {
 		AnalyticsHandler:      analyticsHandler,
 		QueueHandler:          queueHandler,
 		SystemSettingsHandler: systemSettingsHandler,
+		ProcessingIssuesHandler: processingIssuesHandler,
 		CollectionHandler:     collectionHandler,
 		FiltersHandler:        filtersHandler,
 		DashboardHandler:      dashboardHandler,