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/setup.ts

@@ -1,8 +1,9 @@
 import { beforeAll, afterAll } from 'vitest';
 import dotenv from 'dotenv';
+import path from 'path';
 
-// Load environment variables
-dotenv.config({ path: '.env' });
+// Load environment variables from project root
+dotenv.config({ path: path.resolve(process.cwd(), '.env') });
 
 beforeAll(async () => {
   // Global test setup