refactor: unified brand naming to BoosChat

Rebrand all user-facing product name references from legacy
Chinese name to unified "BoosChat" across frontend components,
metadata, test fixtures, and documentation.

cmd/testdata/tag/init.go

@@ -17,11 +17,11 @@ func Init() error {
 		sortNo   int
 	}{
 		{1, 0, "售前", 1},
-		{2, 1, "贝壳AI", 1},
+		{2, 1, "BoosChat", 1},
 		{3, 2, "产品咨询", 1},
 		{4, 2, "购买意向", 1},
 		{5, 0, "售后", 2},
-		{6, 5, "贝壳AI", 1},
+		{6, 5, "BoosChat", 1},
 		{7, 6, "问题反馈", 1},
 		{8, 6, "产品部署", 2},
 		{9, 6, "需求工单", 3},