feat: 版本轨道按分支彻底分开，自测分支不再共用 feature 轨

每个分支各有一条独立轨道（轨道名即分支名，master/main 沿用历史名 release），
轨道类型 kind 只决定构建号行为：release 上架自增、feature 自测不自增。

- branch_track 映射分支 → 轨道名，新增分支自动建同名轨道
- 迁移：旧的共用 release / feature 轨按分支拆开并复制已用构建号，
  拆完没有分支引用的旧共用轨直接删除；无自测分支时保留 feature 轨作模板
- 分支管理页的下拉只改轨道类型（是否自增），不再影响版本号归属
- 打包设置页按分支分块填写版本号

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BJaZ913U5GVdTkYHiRpvDU

CLAUDE.md

@@ -26,7 +26,7 @@ FastAPI + Vue 3 iOS app auto-packaging service. Supports Ad_Hoc and App_Store bu
 - `backend/config.py` — loads .env, defines all config constants
 - `frontend/src/views/` — BuildView, HistoryView, ConfigView
 - `config.json` — runtime config (apps, schemes, servers, upload, branches, versions) managed via web UI
-- Versions are per-track: each release branch has its own track (master/main keeps the historical `release` track, others are named after the branch, e.g. `develop`; build number auto-increments on App_Store), and all self-test branches share the `feature` track (never increments); each branch's track name lives in `config["branch_track"]`, track records in `config["versions"]["tracks"]` carry `kind` (release/feature)
+- 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)
 
 ## Conventions