feat(website): add Nerd Fonts for programming language icons

- Add Monaspace Argon NF font for dev icons
- Update cookbook.yml with unicode codepoints for language icons:
  - TypeScript: \uE628
  - Python: \uE73C
  - C#/.NET: \uF81A
  - Go: \uE626
- Style .lang-tab and .lang-indicator with Nerd Font family

cookbook/cookbook.yml

@@ -11,19 +11,19 @@ cookbooks:
     languages:
       - id: nodejs
         name: Node.js / TypeScript
-        icon: 🟢
+        icon: "\uE628"
         extension: .ts
       - id: python
         name: Python
-        icon: 🐍
+        icon: "\uE73C"
         extension: .py
       - id: dotnet
         name: .NET (C#)
-        icon: 🟣
+        icon: "\uF81A"
         extension: .cs
       - id: go
         name: Go
-        icon: 🔵
+        icon: "\uE626"
         extension: .go
     recipes:
       - id: error-handling