release: v0.2.3 - replace Material-UI icons with Iconify

Replace all Material-UI icon imports with Iconify equivalents to fix plugin loading.
Headlamp provides @iconify/react as a global, not @mui/icons-material.

Icon mappings:
- ErrorOutline → mdi:alert-circle-outline
- ContentCopy → mdi:content-copy
- Visibility → mdi:eye
- VisibilityOff → mdi:eye-off
- CheckCircle → mdi:check-circle
- Error → mdi:alert-circle
- Warning → mdi:alert
- Add → mdi:plus
- Delete → mdi:delete

Also fixed test-setup.ts lint errors (unused parameters).

Tarball checksum: SHA256:5eb6273488fdf337486311c289f8db3aa5f2505ddbe5b9dd5b8c74b1e15f0032

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>

headlamp-sealed-secrets/src/components/DecryptDialog.tsx

@@ -5,8 +5,8 @@
  * Kubernetes Secret (requires RBAC permissions to read secrets)
  */
 
-import { K8s } from '@kinvolk/headlamp-plugin/lib';
 import { Icon } from '@iconify/react';
+import { K8s } from '@kinvolk/headlamp-plugin/lib';
 import {
   Box,
   Button,

headlamp-sealed-secrets/src/components/EncryptDialog.tsx

@@ -5,8 +5,8 @@
  * client-side using the controller's public certificate
  */
 
-import { K8s } from '@kinvolk/headlamp-plugin/lib';
 import { Icon } from '@iconify/react';
+import { K8s } from '@kinvolk/headlamp-plugin/lib';
 import {
   Box,
   Button,