fix: Merge worktree conflict when target branch already checked out

Use a temp branch + update-ref to avoid "already checked out" error
when merging into the default branch. Also show actual branch name
in the Merge & Push button instead of "Default".

apps/web/src/components/review/InitiativeReview.tsx

@@ -214,7 +214,7 @@ export function InitiativeReview({ initiativeId, onCompleted }: InitiativeReview
               ) : (
                 <GitMerge className="h-3.5 w-3.5" />
               )}
-              Merge & Push to Default
+              Merge & Push to {targetBranch || "default"}
             </Button>
           </div>
         </div>