feat: 支持按 Tag 打包，分支管理可添加 Tag

- 分支管理新增「分支 / Tag」类型选择，Tag 存于 config["tags"]，与分支不可重名
- 每个 Tag 与分支一样拥有同名独立版本轨道，默认上架轨
- 打包页按「分支」「Tag」分组选择；任务新增 ref_type 字段记录引用类型
- Tag 打包时 fetch --tags --force 后以游离 HEAD 检出 refs/tags/<tag>
- 历史记录与下载页按类型显示「分支」或「Tag」

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

CLAUDE.md

@@ -27,6 +27,7 @@ FastAPI + Vue 3 iOS app auto-packaging service. Supports Ad_Hoc and App_Store bu
 - `frontend/src/views/` — BuildView, HistoryView, ConfigView
 - `config.json` — runtime config (apps, schemes, servers, upload, branches, versions) managed via web UI
 - Versions are per-branch: every branch owns a track in `config["versions"]["tracks"]`, named after the branch (master/main keeps the historical name `release`); `config["branch_track"]` maps branch → track name, and each track's `kind` is `release` (build number auto-increments on App_Store) or `feature` (never increments)
+- Tags are buildable refs too: `config["tags"]` (names never collide with branches), tracked in `branch_track` like branches (default kind `release`); tasks store the name in `branch` plus `ref_type` (`branch`/`tag`), and tag builds check out `refs/tags/<tag>` detached
 
 ## Conventions