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/node_modules/playwright/lib/agents/playwright-test-generate.prompt.md

@@ -0,0 +1,8 @@
+---
+agent: playwright-test-generator
+description: Generate test plan
+---
+
+Generate tests for the test plan's bullet 1.1 Add item to card.
+
+Test plan: `specs/coverage.plan.md`