refactor!: build with Dart Sass and update Vercel deployment scripts (#746)

* BREAKING CHANGE: refactor with Dart Sass (supplement to #741)

* chore: update .gitignore to include .vercel and .env*.local

* CI: add build script for Hugo site deployment on Vercel

* CI: update build script for Hugo site deployment on Vercel

* refactor: update SCSS layout styles and introduce page-style mixin

* refactor: reorganize SCSS files and improve layout structure

* refactor: rename copy button classes and update related styles

vercel.json

@@ -0,0 +1,10 @@
+{
+  "$schema": "https://openapi.vercel.sh/vercel.json",
+  "version": 2,
+  "regions": ["hkg1"],
+  "framework": "hugo",
+  "installCommand": "pnpm install",
+  "buildCommand": "chmod a+x build.sh && ./build.sh",
+  "outputDirectory": "public",
+  "alias": ["demo.fixit.lruihao.cn", "fixit-demo"]
+}