feat(ui): update hero button text and enhance welcome screen

- Change primary hero button text from "Start Learning" to "Start Vibe Together!" across all language versions to align with project branding
- Update online reading links in README files to point to /welcome.html for better user onboarding
- Enhance WelcomeScreen.vue with improved animation timing and spacing
- Add dynamic SVG wordmark to homepage hero section for visual appeal
- Implement animated color transition for top promo bar
- Remove testing guidelines comment in AGENTS.md as placeholder
- Adjust feature card styling with increased min-height and icon sizes

docs-readme/ja-JP/README.md

@@ -12,11 +12,11 @@
 # Easy-Vibe : 0から1で学ぶVibe Coding
 
 <p align="center">
-  📌 <a href="https://datawhalechina.github.io/easy-vibe/">オンラインで読む (Read Online)</a> · ✨ <a href="https://datawhalechina.github.io/easy-vibe/zh-cn/appendix/">インタラクティブチュートリアル</a>
+  📌 <a href="https://datawhalechina.github.io/easy-vibe/welcome.html">オンラインで読む (Read Online)</a> · ✨ <a href="https://datawhalechina.github.io/easy-vibe/zh-cn/appendix/">インタラクティブチュートリアル</a>
 </p>
 
 <p align="center">
-  <a href="https://datawhalechina.github.io/easy-vibe/">オンラインで読む</a> ·
+  <a href="https://datawhalechina.github.io/easy-vibe/welcome.html">オンラインで読む</a> ·
   <a href="#-コンテンツナビゲーション">学習マップ</a> ·
   <a href="#contact">コミュニティ交流</a>
 </p>