feat(git): rename remote branches atomically via push

Adds a new command to rename remote branches and update tracking refs.
Renaming remote refs is performed atomically using a single push.
The push creates the new remote ref and deletes the old if it succeeds.
The frontend now invokes remote-rename when needed and shows labels.

- Atomic remote rename via push with create/ref and delete
- Frontend supports remote branch renames from the branch panel
- Compare UI now shows labels for remote refs in results

src/lib/git.ts

@@ -133,6 +133,15 @@ export function renameBranch(
   return invoke<GitStatus>("rename_branch", { path, oldBranch, newBranch });
 }
 
+export function renameRemoteBranch(
+  path: string,
+  remote: string,
+  oldBranch: string,
+  newBranch: string,
+): Promise<GitStatus> {
+  return invoke<GitStatus>("rename_remote_branch", { path, remote, oldBranch, newBranch });
+}
+
 export function deleteBranch(path: string, branch: string, force = false): Promise<GitStatus> {
   return invoke<GitStatus>("delete_branch", { path, branch, force });
 }