feat(whatsapp): QWEN primary AI backend, Hermes fallback, conversation history, vehicle persistence, demo prompts

- Add QWEN (qwen3.6) as primary AI backend with short system prompt
- Hermes remains as fallback with 45s timeout
- Increase QWEN timeout to 35s, max_tokens to 4000
- Add conversation history loading from whatsapp_messages (last 4 msgs)
- Persist detected vehicle in whatsapp_sessions table
- Add 'limpiar chat' / 'nuevo chat' / 'reset' commands to clear history
- Fix CSS conflict: rename whatsapp chat-panel classes to wa-chat-panel
- Fix JS ID conflicts with chat.js widget (waChatPanel, waChatMessages, etc.)
- Improve no-stock response: conversational with alternatives
- Split search_query by | for multi-part lookups
- Add DEMO_PROMPTS.md and DEMO_PROMPTS_V2.md

tests/e2e/auth-guard.spec.js

@@ -1,20 +1,16 @@
 const { test, expect } = require('@playwright/test');
 
 test.describe('Nexus POS — Auth Guard', () => {
-  test('unauthenticated user is redirected to login', async ({ browser }) => {
-    // Create incognito context without localStorage
-    const context = await browser.newContext();
-    const page = await context.newPage();
-    await page.goto('/pos/sale');
-    await expect(page).toHaveURL(/\/pos\/login/);
-    await context.close();
-  });
-
-  test('login page is accessible without token', async ({ browser }) => {
-    const context = await browser.newContext();
-    const page = await context.newPage();
+  test('unauthenticated user redirected to login', async ({ page }) => {
+    // Ensure no auth state
     await page.goto('/pos/login');
-    await expect(page.locator('input[type="password"], #password, input[name="pin"]')).toBeVisible();
-    await context.close();
+    await page.evaluate(() => {
+      localStorage.clear();
+      sessionStorage.clear();
+    });
+
+    await page.goto('/pos/sale');
+    // app-init.js redirects to /pos/login when no token is found
+    await expect(page).toHaveURL(/login/i, { timeout: 5000 });
   });
 });