feat(theme): update homepage with Apple-style design and add footer

- Change hero button from "Course Outline" to "GitHub" linking to repository
- Update color scheme to Apple blue gradient and refine button styles
- Add Apple-style footer with localized content, breadcrumb, and policy links
- Introduce top promotional banner with localized call-to-action
- Improve responsive design and adjust spacing for better visual hierarchy

docs/en/index.md

@@ -19,8 +19,8 @@ hero:
       text: Start Learning
       link: /en/stage-0/
     - theme: alt
-      text: Course Outline
-      link: /en/stage-0/
+      text: GitHub
+      link: https://github.com/datawhalechina/easy-vibe
 ---
 
 <HomeFeatures />