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/page-objects/BasePage.ts

@@ -0,0 +1,73 @@
+/**
+ * Base page object with shared helpers.
+ *
+ * All page objects extend this class to inherit common navigation,
+ * waiting, and assertion patterns.
+ */
+
+import { type Page, type Locator, expect } from '@playwright/test';
+
+export abstract class BasePage {
+  constructor(protected readonly page: Page) {}
+
+  /** The path segment for this page (e.g. '/dashboard', '/accounts') */
+  abstract readonly path: string;
+
+  /** Navigate to this page */
+  async goto(): Promise<void> {
+    await this.page.goto(this.path);
+    await this.waitForReady();
+  }
+
+  /**
+   * Override in subclasses to wait for page-specific readiness signals.
+   * Default: waits for network idle.
+   */
+  async waitForReady(): Promise<void> {
+    await this.page.waitForLoadState('networkidle');
+  }
+
+  /** Assert the page URL contains the expected path */
+  async assertOnPage(): Promise<void> {
+    await expect(this.page).toHaveURL(new RegExp(this.path));
+  }
+
+  /** Get the page title text (Mantine AppShell header or h1) */
+  async getPageHeading(): Promise<string> {
+    const heading = this.page.getByRole('heading', { level: 1 }).first();
+    return heading.innerText();
+  }
+
+  /** Wait for a Mantine notification to appear with the given text */
+  async waitForNotification(text: string | RegExp): Promise<void> {
+    await expect(
+      this.page.locator('.mantine-Notification-root').filter({ hasText: text }),
+    ).toBeVisible({ timeout: 10_000 });
+  }
+
+  /** Click a navigation link in the sidebar */
+  async navigateTo(linkText: string): Promise<void> {
+    await this.page.getByRole('link', { name: linkText }).click();
+    await this.page.waitForLoadState('networkidle');
+  }
+
+  /** Get a Mantine table body locator */
+  get tableBody(): Locator {
+    return this.page.locator('tbody');
+  }
+
+  /** Get all table rows */
+  get tableRows(): Locator {
+    return this.tableBody.locator('tr');
+  }
+
+  /** Wait for API response on a specific endpoint pattern */
+  async waitForApi(urlPattern: string | RegExp): Promise<void> {
+    await this.page.waitForResponse(
+      (response) =>
+        (typeof urlPattern === 'string'
+          ? response.url().includes(urlPattern)
+          : urlPattern.test(response.url())) && response.status() < 400,
+    );
+  }
+}