test(service-analytics): keep the selection's granularity a literal type

Claude-Session: https://claude.ai/code/session_01DiCSbmJrkzNhuEAier4VoJ
Co-authored-by: Claude <noreply@anthropic.com>

Author: claude

packages/services/service-analytics/src/__tests__/dataset-selection-window.test.ts

@@ -367,7 +367,7 @@ describe('#3588 — the echoed SQL tells the truth on the ObjectQL path', () =>
         return `driver_bucket('${granularity}', ${field})`;
       },
     });
-    const selection = { dimensions: ['created_at'], measures: ['account_count'], dateGranularity: 'month' };
+    const selection = { dimensions: ['created_at'], measures: ['account_count'], dateGranularity: 'month' as const };
     const result = await svc.queryDataset(accounts, selection, CTX);
     expect(asked).toContain('created_at:month');
     expect(result.sql).toContain(`${DRIVER_BUCKET} AS "created_at"`);