Replace '链接' with 'URL' for clarity in docs

Updated documentation and templates to consistently use 'URL' instead of '链接' when referring to web addresses. This improves clarity and aligns terminology across the README, issue, and pull request templates.

.github/pull_request_template.md

@@ -179,7 +179,7 @@
 
 ## 📸 截图/演示
 
-如果适用，请提供截图或演示链接：
+如果适用，请提供截图或演示 URL：
 
 ## 💬 其他说明