web: scaffold Vue 3 + Vite app (create-vue, lean options)

Verbatim output of 'npm create vue@latest web -- --ts --vitest
--eslint --prettier' so this commit shows exactly what the official
scaffold generates; our own changes come separately. Lean per the
agreed choices: no Router/Pinia until a second page or shared state
exists. node_modules is ignored via the scaffold's own web/.gitignore.

web/vitest.config.ts

@@ -0,0 +1,14 @@
+import { fileURLToPath } from 'node:url'
+import { mergeConfig, defineConfig, configDefaults } from 'vitest/config'
+import viteConfig from './vite.config'
+
+export default mergeConfig(
+  viteConfig,
+  defineConfig({
+    test: {
+      environment: 'jsdom',
+      exclude: [...configDefaults.exclude, 'e2e/**'],
+      root: fileURLToPath(new URL('./', import.meta.url)),
+    },
+  }),
+)