fix: use correct CSS variables for drawer dark mode support

Changed drawer background from var(--mui-palette-background-paper) to
var(--mui-palette-background-default) which properly adapts to dark mode.
Also removed fallback values that were preventing theme variables from
working correctly.

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/components/NamespacesListView.tsx

@@ -103,7 +103,8 @@ function NamespaceDetailPanel({ namespace, onClose }: NamespaceDetailPanelProps)
         top: 0,
         bottom: 0,
         width: '1000px',
-        backgroundColor: 'var(--mui-palette-background-paper, var(--background-paper, #fff))',
+        backgroundColor: 'var(--mui-palette-background-default)',
+        color: 'var(--mui-palette-text-primary)',
         boxShadow: '-2px 0 8px rgba(0,0,0,0.15)',
         overflowY: 'auto',
         zIndex: 1200,
@@ -118,9 +119,7 @@ function NamespaceDetailPanel({ namespace, onClose }: NamespaceDetailPanelProps)
           alignItems: 'center',
         }}
       >
-        <h2
-          style={{ margin: 0, color: 'var(--mui-palette-text-primary, var(--text-primary, #000))' }}
-        >
+        <h2 style={{ margin: 0, color: 'var(--mui-palette-text-primary)' }}>
           Polaris — {namespace}
         </h2>
         <button
@@ -131,7 +130,7 @@ function NamespaceDetailPanel({ namespace, onClose }: NamespaceDetailPanelProps)
             fontSize: '24px',
             cursor: 'pointer',
             padding: '0 8px',
-            color: 'var(--mui-palette-text-primary, var(--text-primary, #000))',
+            color: 'var(--mui-palette-text-primary)',
           }}
           aria-label="Close panel"
         >