feat: add copy button to user messages in chat sidebar (#21)

* Initial plan

* Initial plan for adding copy button to user messages

Co-authored-by: huminglong <63436986+huminglong@users.noreply.github.com>

* Add copy button to user messages in chat sidebar

Co-authored-by: huminglong <63436986+huminglong@users.noreply.github.com>

* Refactor: extract userMessageText to avoid duplicate function calls

Co-authored-by: huminglong <63436986+huminglong@users.noreply.github.com>

* feat(ui): 增加消息复制功能支持非 HTTPS 环境

优化复制消息到剪贴板的逻辑，增加对非 HTTPS 环境的降级处理，提升用户体验。

* fix(package): 添加 peer 属性以支持依赖关系

* chore(.gitignore): 添加 next 和 next-ai-draw-io@0.2.0 相关条目

* fix: improve copy button implementation

- Fix copy button alignment (place left of user message)
- Remove unused React import
- Move getMessageTextContent outside component
- Add error state with X icon for copy failures
- Translate Chinese comments to English
- Simplify copy function
- Add missing semicolon
- Remove accidental .gitignore entries

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: dayuan.jiang <jdy.toh@gmail.com>

.eslintrc.json

@@ -0,0 +1,6 @@
+{
+  "extends": [
+    "next/core-web-vitals",
+    "next/typescript"
+  ]
+}