feat(user): support fixed UUID registration and enhance bulk import results

- Added support for fixed UUIDs during bulk registration (Search-first + ExternalID mapping)
- Implemented idempotency and visibility restoration for soft-deleted users
- Enhanced bulk upload UI to show 'New/Updated/Unchanged' status and modified fields
- Added logic to reclaim identifiers (login_id) from colliding records
- Added frontend E2E and backend unit tests for UUID integrity and conflict handling
- Fixed i18n, formatting, and mock tests to satisfy code-check
- Applied 'go fix' for 'omitzero' tags and general Go standards

backend/cmd/server/main.go

@@ -459,7 +459,7 @@ func main() {
 	app.Use(cors.New(cors.Config{
 		AllowOriginsFunc: func(origin string) bool {
 			// 1. Check static allowed list
-			for _, allowed := range strings.Split(allowedOrigins, ",") {
+			for allowed := range strings.SplitSeq(allowedOrigins, ",") {
 				if origin == strings.TrimSpace(allowed) {
 					return true
 				}
@@ -857,9 +857,9 @@ func main() {
 	// Client Logging Route (Standardized & Flattened)
 	api.Post("/client-log", func(c *fiber.Ctx) error {
 		type LogReq struct {
-			Level   string                 `json:"level"`
-			Message string                 `json:"message"`
-			Data    map[string]interface{} `json:"data,omitempty"`
+			Level   string         `json:"level"`
+			Message string         `json:"message"`
+			Data    map[string]any `json:"data,omitempty"`
 		}
 		var req LogReq
 		if err := c.BodyParser(&req); err != nil {