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

apps/test/content/posts/codeblock-test.md

@@ -18,7 +18,7 @@ Testing code block in FixIt theme.
 🎉🥚 in development mode!
 ```
 
-## Multiple modes
+## Multiple `modes`
 
 ```js {mode="classic"}
 // Classic mode

apps/test/content/posts/mermaid-diagrams-test.md

@@ -13,7 +13,7 @@ tags:
 
 The FixIt theme supports two ways to use Mermaid: code block syntax and shortcode syntax.
 
-```mermaid
+```mermaid {wrapper=false}
 ---
 config:
   theme: 'forest'