chore: upgrade ui and docs frontend dependencies to latest

ui: Vite 8, vue-tsc 3, TypeScript 6, @vitejs/plugin-vue 6, vis-network 10,
vis-data 8, FontAwesome 7, @types/node 25. docs: Vite 8, plugin-vue 6.
Both migrated to Tailwind CSS v4.

- Tailwind v3 -> v4: @import "tailwindcss" with @theme/@config, switch to
  @tailwindcss/postcss, drop autoprefixer (bundled via Lightning CSS).
- docs: move theme into @theme, delete tailwind.config.js, remove stale
  pnpm-lock.yaml (npm/package-lock.json is authoritative).
- ui: TypeScript 6 removes deprecated tsconfig baseUrl; no code changes
  needed for vis-network 10 / FontAwesome 7.
- Bump CI Node 20 -> 22 (Vite 8 requires Node ^20.19 || >=22.12).

0 npm audit vulnerabilities; ui type-check and both production builds pass.

ui/package.json

@@ -10,19 +10,19 @@
     "type-check": "vue-tsc --noEmit"
   },
   "dependencies": {
-    "vis-data": "^7.1.9",
-    "vis-network": "^9.1.9",
-    "vue": "^3.5.13"
+    "vis-data": "^8.0.4",
+    "vis-network": "^10.1.0",
+    "vue": "^3.5.34"
   },
   "devDependencies": {
-    "@fortawesome/fontawesome-free": "^6.7.2",
-    "@types/node": "^22.10.2",
-    "@vitejs/plugin-vue": "^5.2.1",
-    "autoprefixer": "^10.4.20",
-    "postcss": "^8.4.49",
-    "tailwindcss": "^3.4.17",
-    "typescript": "~5.7.2",
-    "vite": "^6.0.5",
-    "vue-tsc": "^2.2.0"
+    "@fortawesome/fontawesome-free": "^7.2.0",
+    "@tailwindcss/postcss": "^4.3.0",
+    "@types/node": "^25.9.1",
+    "@vitejs/plugin-vue": "^6.0.7",
+    "postcss": "^8.5.15",
+    "tailwindcss": "^4.3.0",
+    "typescript": "~6.0.3",
+    "vite": "^8.0.14",
+    "vue-tsc": "^3.3.1"
   }
 }