feat: implement ERP authentication service

Implement ErpAuthService with TDD approach:
- Add login(), close(), getSession(), isActive() methods
- Use Playwright chromium with headless:false for debugging
- Manage browser lifecycle and session state
- Handle authentication flow with ERP_LOCATORS
- Add integration tests for login scenarios
- Add unit tests for session management
- Fix dotenv config path in test setup

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

tests/integration/erp-auth.test.ts

@@ -0,0 +1,40 @@
+import { describe, it, expect, beforeAll, afterAll } from 'vitest';
+import { ErpAuthService } from '../../src/main/services/erp/erp-auth';
+import type { ErpConfig } from '../../src/main/types/erp.types';
+
+describe('ERP Authentication Service (Integration)', () => {
+  let authService: ErpAuthService;
+  const config: ErpConfig = {
+    url: process.env.ERP_URL || '',
+    username: process.env.ERP_USERNAME || '',
+    password: process.env.ERP_PASSWORD || '',
+  };
+
+  beforeAll(() => {
+    if (!config.url || !config.username || !config.password) {
+      throw new Error('Missing ERP credentials in environment variables');
+    }
+    authService = new ErpAuthService(config);
+  });
+
+  it('should login successfully', async () => {
+    const session = await authService.login();
+
+    expect(session).toBeDefined();
+    expect(session.browser).toBeDefined();
+    expect(session.context).toBeDefined();
+    expect(session.page).toBeDefined();
+    expect(session.isLoggedIn).toBe(true);
+  }, 30000);
+
+  it('should navigate to main page after login', async () => {
+    const session = await authService.login();
+
+    const url = session.page.url();
+    expect(url).toContain(config.url);
+  }, 30000);
+
+  afterAll(async () => {
+    await authService?.close();
+  });
+});