chore(docs): release notes 归档 docs/release-notes/ + 根目录汇总 CHANGELOG.md

- 20 份 release-notes-v*.md 移入 docs/release-notes/（git mv 保留历史）
- 新增 CHANGELOG.md：v0.7.1~v0.7.20 倒序浓缩汇总（日期取各文件原始添加提交）
- publish-gitea.sh 与 release.yml 改为 docs/release-notes/<tag>.md 优先、根目录回退

.github/workflows/release.yml

@@ -73,7 +73,8 @@ jobs:
         id: notes
         shell: bash
         run: |
-          FILE="release-notes-${{ github.ref_name }}.md"
+          FILE="docs/release-notes/${{ github.ref_name }}.md"
+          [ -f "$FILE" ] || FILE="release-notes-${{ github.ref_name }}.md"
           {
             echo 'body<<RELEASE_BODY_EOF'
             if [ -f "$FILE" ]; then