fix: change LCP image from png to webp

ch/index.md

@@ -6,7 +6,7 @@ hero:
   name: "Frontend Fundamentals"
   tagline: "易于修改的前端代码指南"
   image:
-    src: /images/ff-symbol-gradient.png
+    src: /images/ff-symbol-gradient-webp-80.webp
     alt: Frontend Fundamentals symbol
   actions:
     - text: 了解好代码的标准

en/index.md

@@ -6,7 +6,7 @@ hero:
   name: "Frontend Fundamentals"
   tagline: "Guidelines for easily modifiable frontend code"
   image:
-    src: /images/ff-symbol-gradient.png
+    src: /images/ff-symbol-gradient-webp-80.webp
     alt: Frontend Fundamentals symbol
   actions:
     - text: Learn about good code

index.md

@@ -6,7 +6,7 @@ hero:
   name: "Frontend Fundamentals"
   tagline: "변경하기 쉬운 프론트엔드 코드를 위한 지침서"
   image:
-    src: /images/ff-symbol-gradient.png
+    src: /images/ff-symbol-gradient-webp-80.webp
     alt: Frontend Fundamentals symbol
   actions:
     - text: 좋은 코드의 기준 알아보기
@@ -25,4 +25,4 @@ features:
   - icon: 📝
     title: 내 코드가 고민된다면
     details: 깃허브 디스커션에서 다른 개발자들과 소통해 보세요.
----
+---

ja/index.md

@@ -6,7 +6,7 @@ hero:
   name: "Frontend Fundamentals"
   tagline: "簡単に変更できるフロントエンドコードのガイドライン"
   image:
-    src: /images/ff-symbol-gradient.png
+    src: /images/ff-symbol-gradient-webp-80.webp
     alt: Frontend Fundamentals symbol
   actions:
     - text: 良いコードについて学ぶ