Scaffold Svelte frontend and browser test matrix

Establish the TypeScript 7, Oxlint, Vitest, and Playwright workspace with an isolated Svelte diagnostics compatibility boundary.

web/playwright.config.ts

@@ -0,0 +1,30 @@
+import { defineConfig, devices } from '@playwright/test'
+
+export default defineConfig({
+  testDir: './tests/e2e',
+  fullyParallel: true,
+  reporter: 'line',
+  use: {
+    baseURL: 'http://127.0.0.1:4173',
+    trace: 'on-first-retry',
+  },
+  webServer: {
+    command: 'pnpm preview --host 127.0.0.1 --port 4173',
+    url: 'http://127.0.0.1:4173',
+    reuseExistingServer: true,
+  },
+  projects: [
+    {
+      name: 'chromium',
+      use: devices['Desktop Chrome'],
+    },
+    {
+      name: 'firefox',
+      use: devices['Desktop Firefox'],
+    },
+    {
+      name: 'webkit',
+      use: devices['Desktop Safari'],
+    },
+  ],
+})