refactor: Retire the use of unmaintained custom-card-helpers (#1956)

- Closes #1295

tests/ha/compute-domain.test.ts

@@ -0,0 +1,26 @@
+import { describe, it, expect } from 'vitest';
+import { computeDomain } from '../../src/ha/compute-domain.js';
+
+describe('computeDomain', () => {
+  it('should return the domain of an entity ID', () => {
+    expect(computeDomain('light.kitchen')).toBe('light');
+    expect(computeDomain('sensor.temperature')).toBe('sensor');
+    expect(computeDomain('switch.garage')).toBe('switch');
+  });
+
+  it('should return an empty string if there is no dot in the entity ID', () => {
+    expect(computeDomain('invalidEntityId')).toBe('');
+  });
+
+  it('should handle entity IDs with multiple dots correctly', () => {
+    expect(computeDomain('light.kitchen.ceiling')).toBe('light');
+  });
+
+  it('should return an empty string for an empty entity ID', () => {
+    expect(computeDomain('')).toBe('');
+  });
+
+  it('should return an empty string for a dot-only entity ID', () => {
+    expect(computeDomain('.')).toBe('');
+  });
+});