fix: fall back to threadRef when draftId is absent in BranchToolbar

When BranchToolbar is rendered for a draft thread without a draftId prop,
selecting a branch silently discarded the user's selection due to an early
return guard. Restore the original behavior by falling back to threadRef
(which is always available) when draftId is not provided.

Author: cursoragent

apps/web/src/components/BranchToolbar.tsx

@@ -105,10 +105,7 @@ export default function BranchToolbar({
         currentWorktreePath: activeWorktreePath,
         effectiveEnvMode,
       });
-      if (!draftId) {
-        return;
-      }
-      setDraftThreadContext(draftId, {
+      setDraftThreadContext(draftId ?? threadRef, {
         branch,
         worktreePath,
         envMode: nextDraftEnvMode,
@@ -124,6 +121,7 @@ export default function BranchToolbar({
       setThreadBranchAction,
       setDraftThreadContext,
       draftId,
+      threadRef,
       environmentId,
       effectiveEnvMode,
     ],