fix: use uvx for Vercel build

Author: LynnGuo666

vercel.json

@@ -1,6 +1,6 @@
 {
   "$schema": "https://openapi.vercel.sh/vercel.json",
-  "buildCommand": "python3 -m pip install --disable-pip-version-check zensical==0.0.57 && zensical build --clean",
+  "buildCommand": "uvx --from zensical==0.0.57 zensical build --clean",
   "outputDirectory": "site",
   "framework": null
 }