docs(workflow): codify the branch model — main / feature / release branches

Adopt GitHub Flow + release branches, replacing "everything straight to main
plus a tag" which caused the 1.4.2 pain (a fix had to be retro-fitted to the
released version, forcing a remote-tag delete + full re-upload).

- main: only long-lived branch, always deployable, accumulates the next version
- feature/<desc>: born from main, merged back when done
- release/vX.Y.Z: cut from main, tagged, installers built from the tag
- hotfixes land on the release branch AND are cherry-picked back to main so
  main never loses a fix
- end of lifecycle = retire the release branch (delete; or keep for long-term
  maintenance), no wholesale merge back — hotfixes already flowed
- explicitly no rebase of main, no release-branch-merge, no quick edits on main

Companion release checklist includes the upload lessons (PUT --http1.1) and the
replace-artifacts-by-deleting-the-tag catch.

Docs in docs/git-workflow.md (zh) and docs/git-workflow-en.md, linked from both
READMEs.

README.md

@@ -490,6 +490,15 @@ internal/gateway         # OpenAI 兼容 HTTP 服务 + 鉴权 + SDK/流式 + Web
 internal/types           # 统一格式 & OpenAI wire 类型
 ```
 
+## 开发协作
+
+- **Git 分支工作流**：主分支 / 特性分支 / 发布分支的规范见
+  **[docs/git-workflow.md](docs/git-workflow.md)**（[English](docs/git-workflow-en.md)）。
+  主线：`main` 永可部署 → 特性合入 `main` → 切 `release/vX.Y.Z` 打 tag 发布 →
+  hotfix 提交发布分支并 cherry-pick 回 `main`。
+- **Lua 适配器协议**：见 **[docs/lua-adapters.md](docs/lua-adapters.md)**
+  （[English](docs/lua-adapters-en.md)）。
+
 ## 测试
 
 ```bash