docs: Update featured guidelines overview

- Enhanced clarity and structure of featured guidelines
- Improved documentation for mini-app developers
- Updated requirements and best practices

Author: claudiahaddad

docs/mini-apps/featured-guidelines/overview.mdx

@@ -52,7 +52,9 @@ Your app must meet all product, design, and technical guidelines outlined below.
 <Step title="App Metadata">
   * App description is clear, concise, and user-focused
   * App icon is **1024×1024 px**, PNG, **no transparency**, readable at small sizes
-  * App cover photo is **high quality** and does not contain Base logo or team photos
+  * App cover photo is **high quality**,does not contain Base logo or team photos, and is 1200×630px (1.91:1) dimensions, PNG/JPG.
+  * Include 3 screenshots that highlight key app functionality. Use portrait orientation with 1284x2778 dimensions. 
+  * Subtitle should be descriptive and specific, and use sentence case capitalization with no punctuation at the end.
 </Step>
 </Steps>