Fix all frontend ESLint errors

- Add eslint-plugin-react-hooks to package.json and config
- Fix duplicate imports in HostsPage.tsx
- Remove non-null assertion in main.tsx
- Fix != to !== in HostDetailPage.tsx and MaintenanceWindowsPage.tsx
- Fix unused variable in ReportsPage.tsx
- Change console.debug to console.warn in useJobWebSocket.ts

frontend/src/pages/ReportsPage.tsx

@@ -126,7 +126,7 @@ export default function ReportsPage() {
       link.click()
       link.remove()
       window.URL.revokeObjectURL(url)
-    } catch (err: unknown) {
+    } catch (_err: unknown) {
       setError('Failed to generate report. Please try again.')
     } finally {
       setDownloading(false)