♻️ refactor(styles): extract fadeIn animation to animations.ts

Extracts the `fadeIn` animation keyframes into a shared `src/styles/animations.ts` file to reduce duplication in `SyntaxHighlighter` and `SyntaxMarkdown`.

Files updated:
- src/styles/animations.ts (new)
- src/Highlighter/SyntaxHighlighter/style.ts
- src/Markdown/SyntaxMarkdown/style.ts

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: Innei

src/Highlighter/SyntaxHighlighter/style.ts

@@ -1,14 +1,7 @@
-import { createStaticStyles, cx, keyframes } from 'antd-style';
+import { createStaticStyles, cx } from 'antd-style';
 import { cva } from 'class-variance-authority';
 
-const fadeIn = keyframes`
-    0% {
-      opacity: 0;
-    }
-    100% {
-      opacity: 1;
-    }
-  `;
+import { fadeIn } from '@/styles/animations';
 
 export const styles = createStaticStyles(({ css, cssVar }) => {
   return {

src/Markdown/SyntaxMarkdown/style.ts

@@ -1,13 +1,6 @@
-import { createStaticStyles, keyframes } from 'antd-style';
+import { createStaticStyles } from 'antd-style';
 
-const fadeIn = keyframes`
-    0% {
-      opacity: 0;
-    }
-    100% {
-      opacity: 1;
-    }
-  `;
+import { fadeIn } from '@/styles/animations';
 
 export const styles = createStaticStyles(({ css }) => {
   return {

src/styles/animations.ts

@@ -0,0 +1,10 @@
+import { keyframes } from 'antd-style';
+
+export const fadeIn = keyframes`
+    0% {
+      opacity: 0;
+    }
+    100% {
+      opacity: 1;
+    }
+`;