Fix duplicate and uncentered loaders on Team Brokers page load

### Description

When accessing the Team Brokers page for the first time, multiple loaders are shown (more obvious on production than on local dev). Additionally:

- The second loader is not centered in the middle of the page
- Switching between the Hierarchy and Clients tabs for the FlowFuse broker also shows a loader that is not centered

Investigate why multiple loaders render on initial load, consolidate to a single loading state, and ensure all loaders (initial load and tab switches) are properly centered.

### Epic/Story

_No response_

### Have you provided an initial effort estimate for this issue?

I have provided an initial effort estimate