fix: replace @mui/icons-material with @iconify/react (v0.2.3)

Material-UI icons were not provided as globals by Headlamp, causing
'undefined is not an object (evaluating Ct.createSvgIcon)' errors.

Headlamp provides @iconify/react as a global, so all icon imports have
been replaced with Iconify equivalents:
- 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

Changes:
- Replaced all @mui/icons-material imports with @iconify/react Icon component
- Updated 4 component files (ErrorBoundary, DecryptDialog, EncryptDialog, ControllerStatus)
- Bumped version to 0.2.3
- Bundle size reduced: 358.18 kB (98.04 kB gzipped)
- Checksum: SHA256:03787323abc9430a63433838253b2dd8296d237000acdfe4ce2507678b63125f

This should fix the plugin loading issue and make the sidebar entry appear.

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/package.json

@@ -1,6 +1,6 @@
 {
   "name": "headlamp-sealed-secrets",
-  "version": "0.2.2",
+  "version": "0.2.3",
   "description": "Headlamp plugin for Bitnami Sealed Secrets - manage encrypted Kubernetes secrets",
   "files": [
     "dist",
@@ -60,6 +60,7 @@
     "node-forge": "^1.3.1"
   },
   "devDependencies": {
+    "@iconify/react": "^6.0.2",
     "@kinvolk/headlamp-plugin": "^0.13.0",
     "@types/node-forge": "^1.3.11",
     "typedoc": "^0.28.16",