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/tsconfig.vitest.json

@@ -0,0 +1,19 @@
+{
+  "extends": "./tsconfig.app.json",
+
+  // Override to include only test files and clear exclusions.
+  // Application code imported in tests is automatically included via module resolution.
+  "include": ["src/**/__tests__/*", "env.d.ts"],
+  "exclude": [],
+
+  "compilerOptions": {
+    // Vitest runs in a different environment than the application code.
+    // Adjust lib and types accordingly.
+    "lib": [],
+    "types": ["node", "jsdom"],
+
+    // `vue-tsc --build` produces a .tsbuildinfo file for incremental type-checking.
+    // Specified here to keep it out of the root directory.
+    "tsBuildInfoFile": "./node_modules/.tmp/tsconfig.vitest.tsbuildinfo"
+  }
+}