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/internal/service/worksmobile_client.go

@@ -737,7 +737,7 @@ type WorksmobileUserPatchPayload struct {
 	DomainID        int64                         `json:"domainId"`
 	Email           string                        `json:"email,omitempty"`
 	UserExternalKey string                        `json:"userExternalKey,omitempty"`
-	UserName        WorksmobileUserName           `json:"userName,omitempty"`
+	UserName        WorksmobileUserName           `json:"userName"`
 	CellPhone       string                        `json:"cellPhone,omitempty"`
 	EmployeeNumber  string                        `json:"employeeNumber,omitempty"`
 	AliasEmails     []string                      `json:"aliasEmails,omitempty"`