Add dockerized Playwright E2E (todo §1); screenshot live pages + foundation mockups, assert shared design-system styles match

e2e/playwright.config.ts

@@ -0,0 +1,20 @@
+import { defineConfig, devices } from "@playwright/test";
+
+// Visual + functional checks against the live app (the `web` compose service, BASE_URL) and the
+// static html-css-foundation mockups (bind-mounted at /repo). Run via compose.e2e.yml. Parallel
+// per the project's E2E principle (todo §1.1); deterministic colorScheme/viewport so the
+// computed-style parity vs the reference design is stable.
+export default defineConfig({
+  testDir: ".",
+  outputDir: "artifacts/test-output",
+  fullyParallel: true,
+  forbidOnly: true,
+  reporter: [["list"], ["html", { open: "never", outputFolder: "artifacts/report" }]],
+  use: {
+    baseURL: process.env.BASE_URL ?? "http://localhost:3000",
+    colorScheme: "light",
+    screenshot: "only-on-failure",
+    viewport: { width: 1280, height: 800 },
+  },
+  projects: [{ name: "chromium", use: { ...devices["Desktop Chrome"] } }],
+});