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>

tests/test_api_config.py

@@ -345,3 +345,37 @@ def test_delete_branch_with_slash_in_name(client, tmp_config):
     resp = client.delete("/api/config/branches/feature%2Flogin")
     assert resp.status_code == 200
     assert "feature/login" not in client.get("/api/config/branches").json()
+
+
+def test_tags_crud_and_default_release_track(client, tmp_config):
+    """Tag 与分支分开存放，默认建一条同名上架轨，可切换类型、可删除"""
+    assert client.get("/api/config/tags").json() == []
+    resp = client.post("/api/config/tags", json={"name": "v3.2.0"})
+    assert resp.status_code == 200
+    assert resp.json()["track"] == "v3.2.0"
+    assert client.get("/api/config/tags").json() == ["v3.2.0"]
+    assert client.get("/api/tags").json() == ["v3.2.0"]
+    assert "v3.2.0" not in client.get("/api/config/branches").json()
+
+    data = client.get("/api/config/versions").json()
+    assert data["branch_track"]["v3.2.0"] == "v3.2.0"
+    assert data["tracks"]["v3.2.0"]["kind"] == "release"
+    # 主上架轨仍按分支判断，Tag 不会抢占
+    assert data["primary_track"] == "release"
+
+    assert client.put("/api/config/branches/track", json={"branch": "v3.2.0", "track": "feature"}).status_code == 200
+    assert client.get("/api/config/versions").json()["tracks"]["v3.2.0"]["kind"] == "feature"
+
+    assert client.delete("/api/config/tags/v3.2.0").status_code == 200
+    assert client.get("/api/config/tags").json() == []
+    assert "v3.2.0" not in client.get("/api/config/versions").json()["branch_track"]
+    assert client.delete("/api/config/tags/v3.2.0").status_code == 404
+
+
+def test_tag_and_branch_names_must_not_collide(client, tmp_config):
+    assert client.post("/api/config/tags", json={"name": ""}).status_code == 400
+    assert client.post("/api/config/tags", json={"name": "main"}).status_code == 400
+    assert client.post("/api/config/tags", json={"name": "release/v1"}).status_code == 200
+    assert client.post("/api/config/tags", json={"name": "release/v1"}).status_code == 400
+    assert client.post("/api/config/branches", json={"name": "release/v1"}).status_code == 400
+    assert client.delete("/api/config/tags/release%2Fv1").status_code == 200