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/vitest.config.ts

@@ -0,0 +1,19 @@
+import { defineConfig } from "vitest/config";
+import react from "@vitejs/plugin-react";
+import path from "path";
+
+export default defineConfig({
+  plugins: [react()],
+  resolve: {
+    alias: {
+      "@fn_library": path.resolve(__dirname, "../../../frontend/functions"),
+    },
+  },
+  test: {
+    environment: "jsdom",
+    globals: true,
+    setupFiles: ["./src/test/setup.ts"],
+    include: ["src/**/*.test.{ts,tsx}"],
+    exclude: ["e2e/**", "node_modules/**"],
+  },
+});