phase 2: ui testing infrastructure

Vitest + @testing-library/jest-dom matchers wired through tests/setup.ts.
Playwright with four projects: chromium-desktop, webkit-desktop,
chromium-mobile-iphone-13, chromium-mobile-pixel-5; traces and
screenshots retained on failure.

.gitea/workflows/ui-test.yaml runs Tier 1 on every push and pull
request: monorepo Go service tests (backend with -p 1 to dodge
testcontainer contention; gateway, game, every pkg/<name> module),
pnpm install --frozen-lockfile, playwright install --with-deps,
pnpm test, pnpm exec playwright test. Uploads playwright-report
and test-results on failure. Integration suite stays gated behind
make -C integration integration; deprecated client/ excluded.

.gitea/workflows/ui-release.yaml mirrors Tier 1 on v* tag push and
keeps commented placeholders for visual regression (Phase 33) and
macOS iOS smoke (Phase 32).

ui/docs/testing.md documents both tiers and the local invocations
that mirror what CI runs. ui/PLAN.md Phase 2 marked done; Phase 3
gains a bullet to extend the go test command with ./ui/core/...;
Phase 36 has the renamed release workflow path.

tools/local-ci/ ships a self-contained docker-compose for verifying
workflows against a local Gitea + arm64 act_runner before pushing
to a real instance.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

ui/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 ? 1 : 0,
+	reporter: [["list"], ["html", { open: "never" }]],
+	use: {
+		baseURL: "http://localhost:5173",
+		trace: "retain-on-failure",
+		screenshot: "only-on-failure",
+	},
+	projects: [
+		{ name: "chromium-desktop", use: { ...devices["Desktop Chrome"] } },
+		{ name: "webkit-desktop", use: { ...devices["Desktop Safari"] } },
+		// devices["iPhone 13"] picks WebKit by default; the project name
+		// here claims a Chromium engine on a mobile viewport, so the
+		// browser is explicitly overridden. WebKit on a desktop viewport
+		// is already covered by webkit-desktop.
+		{
+			name: "chromium-mobile-iphone-13",
+			use: { ...devices["iPhone 13"], browserName: "chromium" },
+		},
+		{ name: "chromium-mobile-pixel-5", use: { ...devices["Pixel 5"] } },
+	],
+	webServer: {
+		command: "pnpm run dev",
+		url: "http://localhost:5173",
+		reuseExistingServer: !process.env.CI,
+		timeout: 120_000,
+	},
+});