feat(git): support credentials for remote branch rename

Allow remote branch renames to be performed with optional credentials so
operations against protected remotes succeed when authentication is needed.
The backend accepts username/password and uses an authenticated push path
when provided, while the frontend prompts for and reuses stored credentials.

- Add optional username/password to rename RPC and use authenticated push
- Wire UI to queue rename, open credential dialog, and execute rename
- Extend credential dialog and handling to include the rename action

src/lib/git.ts

@@ -138,8 +138,17 @@ export function renameRemoteBranch(
   remote: string,
   oldBranch: string,
   newBranch: string,
+  username?: string,
+  password?: string,
 ): Promise<GitStatus> {
-  return invoke<GitStatus>("rename_remote_branch", { path, remote, oldBranch, newBranch });
+  return invoke<GitStatus>("rename_remote_branch", {
+    path,
+    remote,
+    oldBranch,
+    newBranch,
+    username: username ?? null,
+    password: password ?? null,
+  });
 }
 
 export function deleteBranch(path: string, branch: string, force = false): Promise<GitStatus> {