fix: replace useOptimistic with useState for branch selector

useOptimistic requires useTransition/startTransition to persist
optimistic values during async work. Since the concurrency guard
was refactored to use manual useState/useRef, useOptimistic would
flash and immediately revert. Replace with useState + sync effect.

Author: Marve10s

apps/web/src/components/BranchToolbarBranchSelector.tsx

@@ -8,7 +8,6 @@ import {
   useDeferredValue,
   useEffect,
   useMemo,
-  useOptimistic,
   useRef,
   useState,
 } from "react";
@@ -298,10 +297,12 @@ export function BranchToolbarBranchSelector({
       normalizedDeferredBranchQuery,
     ],
   );
-  const [resolvedActiveBranch, setOptimisticBranch] = useOptimistic(
-    canonicalActiveBranch,
-    (_currentBranch: string | null, optimisticBranch: string | null) => optimisticBranch,
-  );
+  const [resolvedActiveBranch, setOptimisticBranch] = useState(canonicalActiveBranch);
+
+  // Sync resolved branch when canonical value changes (e.g., after query invalidation)
+  useEffect(() => {
+    setOptimisticBranch(canonicalActiveBranch);
+  }, [canonicalActiveBranch]);
   const [isBranchActionPending, setIsBranchActionPending] = useState(false);
   const isBranchActionPendingRef = useRef(false);
   const shouldVirtualizeBranchList = filteredBranchPickerItems.length > 40;