feat(e2e): ajouter tests Playwright flux utilisateur core (login, workspace, palette, dashboard)

- e2e/flowdeck_e2e_final.spec.js: 4 tests E2E validés
  1. Login UI local (#email, #password, .btn-primary)
  2. Créer workspace local + entrer (modal .dialog-input)
  3. Ouvrir palette Ctrl+K et valider 'Créer une collection'
  4. Dashboard accessible
- e2e/ : package.json, playwright.config.js, install chromium

e2e/playwright.config.js

@@ -0,0 +1,15 @@
+const { defineConfig } = require('@playwright/test');
+
+module.exports = defineConfig({
+  testDir: '.',
+  timeout: 60000,
+  retries: 0,
+  use: {
+    headless: true,
+    baseURL: process.env.FD_BASE_URL || 'http://localhost:8080',
+    viewport: { width: 1440, height: 900 },
+    screenshot: 'only-on-failure',
+    trace: 'retain-on-failure',
+  },
+  reporter: [['list']],
+});