test(admin): cover expand status dispatch

[overtrue]

Related Issue(s)

None.

Problem Background and User Impact

The recent expansion workflow added rc admin expand status as a post-expansion rebalance command. The existing follow-up coverage verified command parsing, help text, scale start, and expand stop, but the status dispatch path was still untested at the CLI wrapper layer.

Root Cause Summary

admin expand status delegates to the shared rebalance status implementation. Without an integration test, a future regression could accidentally remove or misroute that branch while lower-level rebalance route tests still pass.

Solution Overview

This PR adds one focused non-Windows integration test that runs rc --json admin expand status against the loopback admin test server, asserts the JSON rebalance status payload is returned, and verifies the CLI sends a GET request to /rustfs/admin/v3/rebalance/status.

Test Status

• cargo test -p rustfs-cli --test admin_expand expand_status_dispatches_to_rebalance_status_json -- --nocapture
• make pre-commit

[Copilot]

Pull request overview

This PR adds missing CLI-wrapper integration coverage for the rc admin expand status command to ensure it correctly dispatches to the shared rebalance status endpoint and returns the expected JSON payload.

Changes:

• Adds a new non-Windows integration test that runs rc --json admin expand status <alias> against the loopback admin test server.
• Asserts the command returns JSON containing rebalance status fields and verifies the CLI performs a GET to /rustfs/admin/v3/rebalance/status.

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