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

vitest.config.ts

@@ -0,0 +1,16 @@
+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',
+      globals: true,
+      exclude: [...configDefaults.exclude, 'e2e/**'],
+      root: fileURLToPath(new URL('./', import.meta.url)),
+      css: true,
+    },
+  }),
+)