chore(test): make DIContainer tolerant to missing electron.app for vitest

tests/smoke/di-container.test.ts

@@ -0,0 +1,21 @@
+import { describe, it, expect } from 'vitest';
+import { DIContainer, resolveTemplatePath, resolveSessionDataPath } from '../../apps/companion/main/di-container';
+
+describe('DIContainer (smoke) - test-tolerance', () => {
+  it('constructs without electron.app and exposes path resolvers', () => {
+    // Constructing DIContainer should not throw in plain Node (vitest) environment.
+    expect(() => {
+      // Note: getInstance lazily constructs the container
+      DIContainer.resetInstance();
+      DIContainer.getInstance();
+    }).not.toThrow();
+
+    // Path resolvers should return strings
+    const tpl = resolveTemplatePath();
+    const sess = resolveSessionDataPath();
+    expect(typeof tpl).toBe('string');
+    expect(tpl.length).toBeGreaterThan(0);
+    expect(typeof sess).toBe('string');
+    expect(sess.length).toBeGreaterThan(0);
+  });
+});