fix(webapp): migrate to Tailwind CSS 4 to remove vulnerable braces dependency

package.json

@@ -57,17 +57,15 @@
     "ws": "8.21.0",
     "sharp": "0.35.4",
     "browserslist": "4.28.7",
-    "baseline-browser-mapping": "2.11.0",
-    "postcss-selector-parser": "6.1.3"
+    "baseline-browser-mapping": "2.11.0"
   },
   "devDependencies": {
     "@cloudflare/workers-types": "^4.20260630.1",
     "@preact/preset-vite": "^2.10.5",
+    "@tailwindcss/vite": "^4.3.3",
     "@types/node": "^26.0.1",
-    "autoprefixer": "^10.5.2",
     "opencc-js": "^1.3.2",
-    "postcss": "^8.5.23",
-    "tailwindcss": "^3.4.19",
+    "tailwindcss": "^4.3.3",
     "tsx": "^4.22.4",
     "typescript": "^6.0.3",
     "vite": "^8.1.3",