feat(app): add WGRplane web UI and backend features

- Add Vue 3 frontend with glassmorphism design (Tailwind CSS)
- Add Go backend handlers: auth, webhooks, stats, scheduler, validation
- Add i18n support (EN, ID, ZH)
- Add Swagger docs and API handlers
- Add nftables integration and plugins support
- Remove deprecated go.mod (migrated to wgrplane)

app/frontend/postcss.config.js

@@ -1,6 +1,6 @@
 export default {
   plugins: {
-    tailwindcss: {},
+    '@tailwindcss/postcss': {},
     autoprefixer: {},
   },
 }