feat: move refresh interval to plugin settings

Register plugin settings via registerPluginSettings so the refresh
interval is configurable from Headlamp's plugin config page instead
of being embedded in the main view header.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/api/polaris.ts

@@ -93,6 +93,13 @@ export function countResults(data: AuditData): ResultCounts {
 
 // --- Settings ---
 
+export const INTERVAL_OPTIONS = [
+  { label: '1 minute', value: 60 },
+  { label: '5 minutes', value: 300 },
+  { label: '10 minutes', value: 600 },
+  { label: '30 minutes', value: 1800 },
+];
+
 const STORAGE_KEY = 'polaris-plugin-refresh-interval';
 const DEFAULT_INTERVAL_SECONDS = 300; // 5 minutes