docs: adopt semantic versioning — release 1.27.1 tracks Gitea 1.27.1

Templates were re-checked against the local gitea clone (v1.27.1 tag): all
46 translation keys exist in locale_en-US, all data paths match the official
templates, and all 110 templates render via `go run . preview all` — no
template changes required.

From now on release versions mirror the Gitea version they support:
- COMPATIBILITY.md: quick reference now leads with release 1.27.1
  (max tested Gitea 1.27.1, active), v1.0.x marked superseded; new
  Versioning section documents the scheme
- README: release version in header + versioning bullet
- Tracker workflow PR body: added semantic-versioning release checklist
  (bump Template Release column, tag vX.Y.Z)

Co-Authored-By: Claude <noreply@anthropic.com>

docs/README.zh-CN.md

@@ -80,6 +80,7 @@ cd tools && go run . dev
 
 - **Gitea 1.25+** — v1.25 引入的邮件模板目录结构
 - **最新测试：** Gitea 1.27.1<!-- TRACKER:LATEST-TESTED -->
+- **版本号：** 发布版本与所支持的 Gitea 版本一致 — Gitea 1.27.1 → 模板发布版 1.27.1（详见 [COMPATIBILITY.md](COMPATIBILITY.md)）
 - 与 Gitea 官方模板 100% 兼容 — 详见 [COMPATIBILITY.md](COMPATIBILITY.md)
 
 ## 许可证