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/domain/idp_models.go

@@ -20,7 +20,7 @@ type BrokerUser struct {
 	PhoneNumber    string   `json:"phone_number"`
 	// Attributes stores custom user attributes.
 	// The "required_keys" tag specifies which keys MUST be present in the IDP's schema support.
-	Attributes map[string]interface{} `json:"attributes" required_keys:"grade,department"`
+	Attributes map[string]any `json:"attributes" required_keys:"grade,department"`
 }
 
 // IDPMetadata represents the schema capabilities of an Identity Provider.