fix: remove all MUI dependencies causing plugin load failure

Replace all @mui/material and @mui/icons-material imports with standard
HTML elements and inline styles. This fixes the browser error:
"TypeError: undefined is not an object (evaluating 'q.createSvgIcon')"

The Headlamp plugin environment doesn't provide the full MUI library,
so plugins must use only Headlamp CommonComponents or standard HTML.

Changes:
- AppBarScoreBadge: Replace Chip and ShieldIcon with button and emoji
- DashboardView: Replace Button and RefreshIcon with button and emoji
- ExemptionManager: Replace all MUI form components with HTML equivalents
- PolarisSettings: Replace Button with HTML button

All tests passing (50/50), TypeScript compilation clean, build successful.

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>

src/components/DashboardView.tsx

@@ -8,8 +8,6 @@ import {
   SimpleTable,
   StatusLabel,
 } from '@kinvolk/headlamp-plugin/lib/CommonComponents';
-import { Button } from '@mui/material';
-import { Refresh as RefreshIcon } from '@mui/icons-material';
 import React from 'react';
 import { AuditData, computeScore, countResults, ResultCounts } from '../api/polaris';
 import { usePolarisDataContext } from '../api/PolarisDataContext';
@@ -114,9 +112,25 @@ export default function DashboardView() {
             <span style={{ fontSize: '14px', color: 'var(--mui-palette-text-secondary, #666)' }}>
               Last updated: {formatAuditTime(data.AuditTime)}
             </span>
-            <Button variant="outlined" startIcon={<RefreshIcon />} onClick={refresh} size="small">
-              Refresh
-            </Button>
+            <button
+              onClick={refresh}
+              style={{
+                padding: '6px 16px',
+                backgroundColor: 'transparent',
+                color: '#1976d2',
+                border: '1px solid #1976d2',
+                borderRadius: '4px',
+                cursor: 'pointer',
+                fontSize: '13px',
+                fontWeight: 500,
+                display: 'inline-flex',
+                alignItems: 'center',
+                gap: '4px',
+              }}
+            >
+              <span>🔄</span>
+              <span>Refresh</span>
+            </button>
           </div>
         )}
       </div>