feat: convert namespace detail to right-side drawer panel

Replace the standalone namespace detail route with an inline drawer panel
that slides in from the right when clicking a namespace in the list view.
This provides a more fluid UX without full page navigation.

Changes:
- Namespace detail now opens in a fixed-position right-side panel (600px width)
- Added semi-transparent backdrop that closes the panel when clicked
- Converted namespace links to buttons with proper click handlers
- Removed /polaris/ns/:namespace route and NamespaceDetailView import
- Updated tests to check for buttons instead of links
- Panel includes close button (×) in header

Technical details:
- Uses React state (selectedNamespace) instead of route params
- Panel styled with fixed positioning, z-index layering, and box shadow
- Backdrop at z-index 1100, panel at 1200 to overlay content
- No MUI imports (stays within Headlamp CommonComponents constraint)

Generated with [Claude Code](https://claude.ai/code)
via [Happy](https://happy.engineering)

Co-Authored-By: Claude <noreply@anthropic.com>
Co-Authored-By: Happy <yesreply@happy.engineering>

src/index.tsx

@@ -6,7 +6,6 @@ import {
 import React from 'react';
 import { PolarisDataProvider } from './api/PolarisDataContext';
 import DashboardView from './components/DashboardView';
-import NamespaceDetailView from './components/NamespaceDetailView';
 import NamespacesListView from './components/NamespacesListView';
 import PolarisSettings from './components/PolarisSettings';
 
@@ -62,16 +61,4 @@ registerRoute({
   ),
 });
 
-registerRoute({
-  path: '/polaris/ns/:namespace',
-  sidebar: 'polaris-namespaces',
-  name: 'polaris-namespace',
-  exact: true,
-  component: () => (
-    <PolarisDataProvider>
-      <NamespaceDetailView />
-    </PolarisDataProvider>
-  ),
-});
-
 registerPluginSettings('polaris', PolarisSettings, true);