add auto-signup login and localized auth UI

- backend: userLogin auto-registers missing users and returns auto_registered
- frontend: add responsive auth page (login + signup flow via userLogin) with light/dark mode and logo
- i18n: wire language switching, add translations for cs/en/es/de
- ui/tooling: add Font Awesome integration

frontend/vite.config.ts

@@ -4,6 +4,9 @@ import { defineConfig } from 'vite'
 import vue from '@vitejs/plugin-vue'
 import vueDevTools from 'vite-plugin-vue-devtools'
 
+import pkg from './package.json';
+
+
 // https://vite.dev/config/
 export default defineConfig({
   plugins: [