test: add Playwright E2E test suite (30 tests)

Add browser-level end-to-end tests covering public pages, Keycloak
OAuth authentication flow, dashboard interactions, providers config,
developer section, organization pages, and sidebar navigation.

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

e2e/auth.setup.ts

@@ -0,0 +1,24 @@
+import { test as setup, expect } from "@playwright/test";
+
+const AUTH_FILE = "e2e/.auth/user.json";
+
+setup("authenticate via Keycloak", async ({ page }) => {
+  // Navigate to a protected route to trigger the auth redirect chain:
+  // /dashboard -> /auth (Axum) -> Keycloak login page
+  await page.goto("/dashboard");
+
+  // Wait for Keycloak login form to appear
+  await page.waitForSelector("#username", { timeout: 15_000 });
+
+  // Fill Keycloak credentials
+  await page.fill("#username", process.env.TEST_USER ?? "admin@certifai.local");
+  await page.fill("#password", process.env.TEST_PASSWORD ?? "admin");
+  await page.click("#kc-login");
+
+  // Wait for redirect back to the app dashboard
+  await page.waitForURL("**/dashboard", { timeout: 15_000 });
+  await expect(page.locator(".sidebar")).toBeVisible();
+
+  // Persist authenticated state (cookies + localStorage)
+  await page.context().storageState({ path: AUTH_FILE });
+});