fix(e2e): replace VITE_MOCK_AUTH with Playwright route mocking

- Removed VITE_MOCK_AUTH=true from playwright.config.ts webServer command
- Added mockAuthRoutes helper to e2e/fixtures.ts to mock /auth/* endpoints
- Updated j1-registration-login.spec.ts to use route mocking instead
  of env var-based mock auth

Co-Authored-By: Paperclip <noreply@paperclip.ing>

e2e/journeys/j1-registration-login.spec.ts

@@ -1,9 +1,11 @@
 import { test, expect } from '@playwright/test';
+import { mockAuthRoutes } from '../fixtures';
 
 const uniqueEmail = () => `betty+e2e-${Date.now()}@cartsnitch.test`;
 
 test.describe('J1: Registration and Login', () => {
   test('can register a new account and lands on dashboard', async ({ page }) => {
+    mockAuthRoutes(page, true);
     await page.goto('/register');
     await page.fill('[placeholder="Full Name"]', 'Betty Tester');
     await page.fill('[placeholder="Email"]', uniqueEmail());
@@ -30,8 +32,8 @@ test.describe('J1: Registration and Login', () => {
   });
 
   test('can sign in with credentials and land on dashboard', async ({ page }) => {
-    // Register first so we have a real account
     const email = uniqueEmail();
+    mockAuthRoutes(page, true);
     await page.goto('/register');
     await page.fill('[placeholder="Full Name"]', 'Login Betty');
     await page.fill('[placeholder="Email"]', email);
@@ -39,11 +41,9 @@ test.describe('J1: Registration and Login', () => {
     await page.click('button[type="submit"]');
     await expect(page).toHaveURL('http://localhost:5173/');
 
-    // Sign out by clearing the mock session (reload with no session)
     await page.goto('/');
     await page.reload();
 
-    // Now sign in
     await page.goto('/login');
     await page.fill('[placeholder="Email"]', email);
     await page.fill('[placeholder="Password"]', 'TestPass123!');