feat(kanban): requester input empty + keyboard nav (issue 0088)

CardForm: drop pre-fill of requester from logged user; Enter inside the
Autocomplete no longer submits the form (Mantine handles dropdown
selection; arrows + Enter pick option without closing modal). Submit
remains via "Crear" button or Ctrl+Enter from description.

Adds data-field="requester" and data-test="add-card" selectors for stable
e2e queries.

Tests:
- vitest component test (CardForm.test.tsx): empty input, Enter does not
  submit, submit only via button. Dropdown arrow nav covered by e2e
  (jsdom portal handling is brittle).
- Playwright e2e (requester-input.spec.ts) using new browser capability
  group (pw_kanban_login, pw_keyboard_sequence) from registry.
- seed_e2e_user CLI to create deterministic test user against
  operations.db (bcrypt via standard backend hash).

Setup additions (frontend/):
- vitest + @testing-library + jsdom devDeps
- @playwright/test devDep + playwright.config.ts
- src/test/setup.ts polyfills jsdom for Mantine (matchMedia,
  visualViewport, document.fonts, ResizeObserver)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

frontend/package.json

@@ -6,7 +6,9 @@
   "scripts": {
     "dev": "vite",
     "build": "tsc -b && vite build",
-    "preview": "vite preview"
+    "preview": "vite preview",
+    "test": "vitest run",
+    "test:e2e": "playwright test"
   },
   "dependencies": {
     "@dnd-kit/core": "^6.3.1",
@@ -30,12 +32,19 @@
     "remark-gfm": "^4.0.1"
   },
   "devDependencies": {
+    "@playwright/test": "^1.60.0",
+    "@testing-library/jest-dom": "^6.9.1",
+    "@testing-library/react": "^16.3.2",
+    "@testing-library/user-event": "^14.6.1",
     "@types/react": "^19.1.6",
     "@types/react-dom": "^19.1.6",
     "@vitejs/plugin-react": "^4.5.2",
+    "@vitest/ui": "^4.1.6",
+    "jsdom": "^29.1.1",
     "postcss": "^8.5.4",
     "postcss-preset-mantine": "^1.17.0",
     "typescript": "~5.8.3",
-    "vite": "^6.3.5"
+    "vite": "^6.3.5",
+    "vitest": "^4.1.6"
   }
 }