Add PWA service worker (via vite plugin), use dynamic viewport units for interface size (improves mobile experience), replace default vue homepage with basic info

frontend/package.json

@@ -9,6 +9,7 @@
     "preview": "vite preview"
   },
   "dependencies": {
+    "vite-plugin-pwa": "^1.0.2",
     "vue": "^3.5.17",
     "vue-router": "^4.5.1"
   },