Phase 5.4-5.11: Playwright E2E test infrastructure with 7 spec files

- playwright.config.ts: chromium project, webServer, baseURL, trace/screenshot/video
- e2e/helpers.ts: API mock setup, login/logout helpers, mock data for all entities
- 7 E2E spec files (1164 lines total):
  - auth.spec.ts: login/logout workflow
  - contact-crud.spec.ts: create/edit/delete contacts, add persons
  - search.spec.ts: global search, filter, results
  - plugin-toggle.spec.ts: enable/disable plugins, UI changes
  - mail.spec.ts: mail account setup, folders, mail viewing
  - dms.spec.ts: folder creation, file upload, preview, share
  - calendar.spec.ts: appointment creation, calendar switch, kanban view
- @playwright/test added as devDependency
- e2e scripts added to package.json
- TSC: 0 new errors (only pre-existing Dms.tsx)

frontend/playwright.config.ts

@@ -0,0 +1,45 @@
+import { defineConfig, devices } from '@playwright/test';
+
+/**
+ * Playwright E2E configuration for LeoCRM.
+ *
+ * Tests run against the Vite dev server (or a preview build).
+ * In CI/CD, set BASE_URL to point at the deployed frontend.
+ */
+export default defineConfig({
+  testDir: './e2e',
+  fullyParallel: true,
+  forbidOnly: !!process.env.CI,
+  retries: process.env.CI ? 2 : 0,
+  workers: process.env.CI ? 1 : undefined,
+  reporter: process.env.CI ? 'github' : 'html',
+  timeout: 30_000,
+  expect: {
+    timeout: 10_000,
+  },
+
+  use: {
+    baseURL: process.env.BASE_URL ?? 'http://localhost:5173',
+    trace: 'on-first-retry',
+    screenshot: 'only-on-failure',
+    video: 'retain-on-failure',
+    locale: 'de-DE',
+    timezoneId: process.env.TZ ?? 'Europe/Berlin',
+  },
+
+  projects: [
+    {
+      name: 'chromium',
+      use: { ...devices['Desktop Chrome'] },
+    },
+  ],
+
+  webServer: process.env.CI
+    ? undefined
+    : {
+        command: 'npm run dev',
+        url: 'http://localhost:5173',
+        reuseExistingServer: !process.env.CI,
+        timeout: 60_000,
+      },
+});