feat: Improve delete API with clear hard delete option

- Single clear way to hard delete: { hard: true }
- Removed confusing soft: false option
- Soft delete remains the default behavior
- Clean, intuitive API: delete() for soft, delete(id, { hard: true }) for hard
- All delete features working: soft, hard, cascade

tests/unified-api.test.ts

@@ -187,7 +187,7 @@ describe('Brainy 1.0 Unified API', () => {
 
     it('should hard delete when specified', async () => {
       const id = await brainy.add("Data to hard delete")
-      const success = await brainy.delete(id, { soft: false })
+      const success = await brainy.delete(id, { hard: true })
       expect(success).toBe(true)
     })