feat(sync): add parallel sync, fix default branch and protected branch issues, add group avatars option

- Set sync concurrency to 10 for faster parallel repo syncing
- Three-phase push: push refs, sync default_branch via API, then push with --prune
- Unprotect stale protected branches on target before pruning
- Handle group visibility 400 errors gracefully (skip visibility, sync description only)
- Add useGroupAvatarsForProjects option: projects without avatars inherit group avatar
- Upgrade @apiclient.xyz/gitlab to v2.3.0 (getProtectedBranches, unprotectBranch)

ts_web/appstate.ts

@@ -742,6 +742,7 @@ export const createSyncConfigAction = syncStatePart.createAction<{
   enforceDelete?: boolean;
   enforceGroupDelete?: boolean;
   addMirrorHint?: boolean;
+  useGroupAvatarsForProjects?: boolean;
 }>(async (statePartArg, dataArg) => {
   const context = getActionContext();
   try {
@@ -769,6 +770,7 @@ export const updateSyncConfigAction = syncStatePart.createAction<{
   enforceDelete?: boolean;
   enforceGroupDelete?: boolean;
   addMirrorHint?: boolean;
+  useGroupAvatarsForProjects?: boolean;
 }>(async (statePartArg, dataArg) => {
   const context = getActionContext();
   try {