feat(alerts/ui): add severityToAccent helper for DataTable rowAccent

Pure function mapping the 3-value AlertDto.severity enum to the 2-value
DataTable rowAccent prop. INFO maps to undefined (no tint) because the
DS DataTable rowAccent only supports error|warning.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

ui/src/pages/Alerts/severity-utils.test.ts

@@ -0,0 +1,16 @@
+import { describe, it, expect } from 'vitest';
+import { severityToAccent } from './severity-utils';
+
+describe('severityToAccent', () => {
+  it('maps CRITICAL → error', () => {
+    expect(severityToAccent('CRITICAL')).toBe('error');
+  });
+
+  it('maps WARNING → warning', () => {
+    expect(severityToAccent('WARNING')).toBe('warning');
+  });
+
+  it('maps INFO → undefined (no row tint)', () => {
+    expect(severityToAccent('INFO')).toBeUndefined();
+  });
+});