NamespaceBar flickering after creating a new namespace

## Description

When selecting a new namespace in the **Kuadrant Overview** page via the `NamespaceBar`, the **namespace selection flickers.** The page briefly shows the new namespace, then flickers the previous namespace, jumps back to the previous resources/namespace.

### Steps to Reproduce

1. Navigate to Kuadrant → Overview
2. Note the currently selected namespace in the NamespaceBar
3. Click on the NamespaceBar dropdown and select **"Create namespace"**
4. Enter a name for the new namespace and create it
5. Observe the page content during the transition after the new namespace is created

### Expected behavior

- After creating the new namespace, the Overview page should immediately switch to show the newly created namespace
- The transition should be smooth and direct
- The new namespace should appear in the NamespaceBar and remain stable
- Gateway counts, policy lists, and HTTPRoutes for the new (empty) namespace should display once

### Actual behavior

- The new namespace's resources briefly appear
- The page flickers back to the previous namespace for ~1 second
- The page finally settles on the previous namespace

### Screenshots

https://github.com/user-attachments/assets/329de62f-7e51-467a-9100-d8e599ac500b

**Affected Files:**
- src/components/KuadrantOverviewPage.tsx
- src/hooks/useKuadrantNamespaceChange.ts

**Related Issues:**
#824 (namespace switching crashes) — Different issue but both involve namespace transition lifecycle