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/vi-VN/README.md

@@ -12,11 +12,11 @@
 # Easy-Vibe : Học Vibe Coding từ 0 đến 1
 
 <p align="center">
-  📌 <a href="https://datawhalechina.github.io/easy-vibe/">Đọc trực tuyến (Read Online)</a> · ✨ <a href="https://datawhalechina.github.io/easy-vibe/zh-cn/appendix/">Hướng dẫn tương tác</a>
+  📌 <a href="https://datawhalechina.github.io/easy-vibe/welcome.html">Đọc trực tuyến (Read Online)</a> · ✨ <a href="https://datawhalechina.github.io/easy-vibe/zh-cn/appendix/">Hướng dẫn tương tác</a>
 </p>
 
 <p align="center">
-  <a href="https://datawhalechina.github.io/easy-vibe/">Đọc trực tuyến</a> ·
+  <a href="https://datawhalechina.github.io/easy-vibe/welcome.html">Đọc trực tuyến</a> ·
   <a href="#-điều-hướng">Bản đồ học tập</a> ·
   <a href="#contact">Cộng đồng</a>
 </p>