feat: add Playwright E2E test config and basic tests

Adds playwright.config.ts pointing at tests/e2e/ with a 15s timeout and dev server reuse. Stubs two test files: public-pages (home, pets, login load checks) and admin-guard (unauthenticated /admin and /foster redirect to /login). Installs @playwright/test as a dev dependency.

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

playwright.config.ts

@@ -0,0 +1,14 @@
+import { defineConfig } from '@playwright/test';
+
+export default defineConfig({
+	testDir: 'tests/e2e',
+	timeout: 15000,
+	webServer: {
+		command: 'npm run dev',
+		port: 5173,
+		reuseExistingServer: true
+	},
+	use: {
+		baseURL: 'http://localhost:5173'
+	}
+});