feat: migrate to unplugin-vue-router for file-based routing

[rileychh]

This PR migrates the project from manual route configuration to unplugin-vue-router for automatic file-based routing.

Changes

• Replace manual src/routes.ts with file-based routing from src/pages/ directory
• Add unplugin-vue-router plugin and configure VueRouter plugin in vite config
• Implement SSG route generation for language-specific pages (en, zh)
• Add typed route definitions with auto-generated typed-router.d.ts
• Create initial page structure with language parameter routing (/[lang]/)

Technical Details

• Routes are now automatically generated from the src/pages/ directory structure
• The includedRoutes function in ssgOptions expands dynamic :lang routes into concrete paths for SSG build
• Supports English (en) and Traditional Chinese (zh) languages