feat: add Playwright E2E testing setup with POM and testids

- Install @playwright/test and Chromium browser
- Create playwright.config.ts with dev server integration
- Add data-testid attributes to LoginPage, DashboardPage, ServerCard, Sidebar
- Exclude tests-e2e from vitest config
- Create Page Object Models: LoginPage, DashboardPage
- Add 18 E2E tests: 6 login flow, 12 dashboard (happy, empty, error states)
- Add test:e2e and test:e2e:ui scripts to package.json

frontend/playwright.config.ts

@@ -0,0 +1,33 @@
+import { defineConfig, devices } from "@playwright/test";
+
+export default defineConfig({
+  testDir: "./tests-e2e",
+  fullyParallel: true,
+  forbidOnly: !!process.env.CI,
+  retries: process.env.CI ? 2 : 0,
+  workers: process.env.CI ? 1 : undefined,
+  reporter: [
+    ["html", { outputFolder: "playwright-report" }],
+    ["list"],
+  ],
+  use: {
+    baseURL: process.env.BASE_URL || "http://localhost:5173",
+    trace: "on-first-retry",
+    screenshot: "only-on-failure",
+    video: "retain-on-failure",
+    actionTimeout: 10_000,
+    navigationTimeout: 30_000,
+  },
+  projects: [
+    {
+      name: "chromium",
+      use: { ...devices["Desktop Chrome"] },
+    },
+  ],
+  webServer: {
+    command: "npm run dev",
+    url: "http://localhost:5173",
+    reuseExistingServer: !process.env.CI,
+    timeout: 120_000,
+  },
+});