Use replaceBranchInStackSelection in stackService

Update stackService to enhance branch name replacement logic by using replaceBranchInStackSelection helper when updating stack selection state. This avoids unnecessary double wrapping and ensures consistency with exclusive action branch name updates.

Author: estib-vega

apps/desktop/src/lib/stacks/stackService.svelte.ts

@@ -12,7 +12,11 @@ import {
 	providesList,
 	ReduxTag
 } from '$lib/state/tags';
-import { replaceBranchInExclusiveAction, type UiState } from '$lib/state/uiState.svelte';
+import {
+	replaceBranchInExclusiveAction,
+	replaceBranchInStackSelection,
+	type UiState
+} from '$lib/state/uiState.svelte';
 import { isDefined } from '@gitbutler/ui/utils/typeguards';
 import {
 	createEntityAdapter,
@@ -615,12 +619,16 @@ export class StackService {
 				const stackState = this.uiState.stack(args.stackId);
 				const projectState = this.uiState.project(args.projectId);
 				const exclusiveAction = projectState.exclusiveAction.current;
-				const previousSelection = stackState.selection.current ?? {};
+				const previousSelection = stackState.selection.current;
 
-				stackState.selection.set({
-					...previousSelection,
-					branchName: args.newName
-				});
+				if (previousSelection) {
+					const updatedSelection = replaceBranchInStackSelection(
+						previousSelection,
+						args.branchName,
+						args.newName
+					);
+					stackState.selection.set(updatedSelection);
+				}
 
 				if (exclusiveAction) {
 					const updatedExclusiveAction = replaceBranchInExclusiveAction(