feat: initialise Vue 3 SPA template

- Add Tailwind CSS v4 with light/dark theme support
- Add layout system (default, sidebar, blank)
- Add mock authentication with Pinia store and route guards
- Add error pages (404, 500) and example views
- Add Vitest with 10 example tests across stores
- Configure Prettier formatting and ESLint linting

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"
+  }
+}