fix(gantt): preserve query parameters when closing task modal

When closing a task modal opened from the Gantt view, the date range
query parameters were lost because closeModal() reconstructed the
route with only projectId and viewId. Now preserves query parameters
from the backdrop view.

frontend/src/composables/useRouteWithModal.ts

@@ -79,12 +79,15 @@ export function useRouteWithModal() {
 
 			// Only navigate if we have a valid project and view
 			if (baseStore.currentProject.id && viewId) {
+				// Preserve query parameters (e.g., date range) from the backdrop view
+				const backdropRoute = historyState.value?.backdropView && router.resolve(historyState.value.backdropView)
 				const newRoute = {
 					name: 'project.view',
 					params: {
 						projectId: baseStore.currentProject.id,
 						viewId,
 					},
+					query: backdropRoute?.query || {},
 				}
 
 				router.push(newRoute)