feat(backlog): add branchName support to apply handler and UI components

- Updated apply handler to accept an optional branchName from the request body.
- Modified BoardView and BacklogPlanDialog components to pass currentBranch to the apply API.
- Enhanced ElectronAPI and HttpApiClient to include branchName in the apply method.

This change allows users to specify a branch when applying backlog plans, improving flexibility in feature management.

apps/ui/src/components/views/board-view.tsx

@@ -1449,6 +1449,7 @@ export function BoardView() {
         setPendingPlanResult={setPendingBacklogPlan}
         isGeneratingPlan={isGeneratingPlan}
         setIsGeneratingPlan={setIsGeneratingPlan}
+        currentBranch={selectedWorktreeBranch}
       />
 
       {/* Plan Approval Dialog */}