feat: add Playwright E2E and API regression test suite

Production-ready test infrastructure with Page Object Model pattern,
reusable fixtures for auth/DB/test-data, and example tests covering
login flow, dashboard, accounts CRUD API, and visual regression.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

tests/auth.setup.ts

@@ -0,0 +1,50 @@
+/**
+ * Auth setup project — runs ONCE before all browser-based tests.
+ *
+ * Logs in via the UI, then saves the authenticated browser state
+ * (cookies + localStorage) to tests/.auth/user.json so that every
+ * subsequent test starts already logged in.
+ *
+ * This matches Playwright's recommended "global setup via project
+ * dependencies" pattern.
+ */
+
+import { test as setup, expect } from '@playwright/test';
+import { TEST_USERS } from './fixtures/test-data';
+import path from 'path';
+
+const authFile = path.join(__dirname, '.auth', 'user.json');
+
+setup('authenticate as test treasurer', async ({ page }) => {
+  // Navigate to login page
+  await page.goto('/login');
+
+  // Fill login form — uses Mantine component labels
+  await page.getByLabel('Email').fill(TEST_USERS.treasurer.email);
+  await page.getByLabel('Password').fill(TEST_USERS.treasurer.password);
+
+  // Submit
+  await page.getByRole('button', { name: 'Sign in' }).click();
+
+  // Wait for redirect away from login page.
+  // After login, the app redirects to /select-org (multi-org) or /dashboard.
+  await page.waitForURL(/\/(select-org|dashboard|admin|onboarding)/, {
+    timeout: 15_000,
+  });
+
+  // If we land on org selection, pick the first org
+  if (page.url().includes('/select-org')) {
+    // Click the first organization card/button
+    const orgButton = page.getByRole('button').first();
+    if (await orgButton.isVisible({ timeout: 3_000 }).catch(() => false)) {
+      await orgButton.click();
+      await page.waitForURL(/\/dashboard/, { timeout: 10_000 });
+    }
+  }
+
+  // Verify we're authenticated — page should not be on /login
+  expect(page.url()).not.toContain('/login');
+
+  // Save authenticated state
+  await page.context().storageState({ path: authFile });
+});