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/src/components/ErrorBoundary.tsx

@@ -4,7 +4,7 @@
  * Provides graceful error handling for crypto and API operations
  */
 
-import { ErrorOutline } from '@mui/icons-material';
+import { Icon } from '@iconify/react';
 import { Alert, Box, Button, Typography } from '@mui/material';
 import React, { Component, ReactNode } from 'react';
 
@@ -71,7 +71,7 @@ export class CryptoErrorBoundary extends BaseErrorBoundary {
       <Box p={3}>
         <Alert
           severity="error"
-          icon={<ErrorOutline />}
+          icon={<Icon icon="mdi:alert-circle-outline" />}
           action={
             <Button color="inherit" size="small" onClick={this.handleReset}>
               Retry
@@ -116,7 +116,7 @@ export class ApiErrorBoundary extends BaseErrorBoundary {
       <Box p={3}>
         <Alert
           severity="error"
-          icon={<ErrorOutline />}
+          icon={<Icon icon="mdi:alert-circle-outline" />}
           action={
             <Button color="inherit" size="small" onClick={this.handleReset}>
               Retry
@@ -163,7 +163,7 @@ export class GenericErrorBoundary extends BaseErrorBoundary {
       <Box p={3}>
         <Alert
           severity="error"
-          icon={<ErrorOutline />}
+          icon={<Icon icon="mdi:alert-circle-outline" />}
           action={
             <Button color="inherit" size="small" onClick={this.handleReset}>
               Reload