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.app.json

@@ -0,0 +1,18 @@
+{
+  "extends": "@vue/tsconfig/tsconfig.dom.json",
+  "include": ["env.d.ts", "src/**/*", "src/**/*.vue"],
+  "exclude": ["src/**/__tests__/*"],
+  "compilerOptions": {
+    // Extra safety for array and object lookups, but may have false positives.
+    "noUncheckedIndexedAccess": true,
+
+    // Path mapping for cleaner imports.
+    "paths": {
+      "@/*": ["./src/*"]
+    },
+
+    // `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.app.tsbuildinfo"
+  }
+}