feat(remote): support authenticated deletion of remote branches

Add support for authenticated deletion of remote branches and folders.
The backend adds a batch delete command that queries the remote,
performs an atomic push --delete when possible with a fallback, and
prunes stale tracking refs; it accepts optional credentials. The
frontend and JS API integrate credential handling and prompt users when
authentication is required.

- New batch deletion command with optional username/password for auth.
- Uses ls-remote to scope deletions, tries --atomic then falls back.
- Frontend updates: credential dialog/action, pendingRemoteDelete state.

src/lib/git.ts

@@ -107,7 +107,12 @@ export function removeRemote(path: string, name: string): Promise<GitRemote[]> {
   console.log("remove_remote")
   return invoke("remove_remote", { path, name }); }
 export function setBranchUpstream(path: string, branch: string, upstream?: string): Promise<GitStatus> { return invoke("set_branch_upstream", { path, branch, upstream: upstream || null }); }
-export function deleteRemoteBranch(path: string, remote: string, branch: string): Promise<GitStatus> { return invoke("delete_remote_branch", { path, remote, branch }); }
+export function deleteRemoteBranch(path: string, remote: string, branch: string, username?: string, password?: string): Promise<GitStatus> {
+  return invoke("delete_remote_branch", { path, remote, branch, username: username ?? null, password: password ?? null });
+}
+export function deleteRemoteBranches(path: string, remote: string, branches: string[], username?: string, password?: string): Promise<GitStatus> {
+  return invoke("delete_remote_branches", { path, remote, branches, username: username ?? null, password: password ?? null });
+}
 
 export function listStashes(path: string): Promise<GitStash[]> {
   return invoke<GitStash[]>("list_stashes", { path });