fix(user): preserve multi-tenant companyCodes and fix Kratos code parsing

- UpdateUser: Implement 'Preserve & Merge' logic to fetch existing joined
  tenants from Keto and merge them with UI requests, preventing the
  loss of multi-tenant affiliations.
- Keto Sync: Expand the self-healing background job to iterate over all
  companyCodes, ensuring 'members' relations are created for every
  joined tenant (fixes #554).
- AuthHandler: Update extractFirstString to gracefully handle numeric
  JSON types, fixing an issue where Kratos login codes were lost during
  Courier webhook processing.

backend/internal/handler/auth_handler.go

@@ -3767,6 +3767,13 @@ func extractFirstString(data map[string]interface{}, keys ...string) string {
 			if str, ok := val.(string); ok && str != "" {
 				return str
 			}
+			// Handle numeric types by converting to string
+			if num, ok := val.(float64); ok {
+				return fmt.Sprint(num)
+			}
+			if num, ok := val.(int); ok {
+				return fmt.Sprint(num)
+			}
 		}
 	}
 	return ""

backend/internal/handler/user_handler.go

@@ -1266,6 +1266,25 @@ func (h *UserHandler) UpdateUser(c *fiber.Ctx) error {
 	if traits == nil {
 		traits = map[string]interface{}{}
 	}
+
+	// [Preserve & Merge] Multi-Tenant Info
+	var existingCodes []string
+	if codes, ok := traits["companyCodes"].([]interface{}); ok {
+		for _, v := range codes {
+			if str, ok := v.(string); ok && str != "" {
+				existingCodes = append(existingCodes, str)
+			}
+		}
+	}
+	// Keto에서 "실제" 소속 정보를 먼저 확인 (엑셀 임포트 사용자 대응)
+	if len(existingCodes) <= 1 && h.TenantService != nil {
+		if joined, err := h.TenantService.ListJoinedTenants(c.Context(), userID); err == nil {
+			for _, t := range joined {
+				existingCodes = append(existingCodes, t.Slug)
+			}
+		}
+	}
+
 	if req.Name != nil {
 		traits["name"] = strings.TrimSpace(*req.Name)
 	}
@@ -1286,7 +1305,33 @@ func (h *UserHandler) UpdateUser(c *fiber.Ctx) error {
 				traits["tenant_id"] = tenant.ID
 			}
 		}
+		
+		// Add to existingCodes if not present
+		found := false
+		for _, existing := range existingCodes {
+			if existing == code {
+				found = true
+				break
+			}
+		}
+		if !found && code != "" {
+			existingCodes = append(existingCodes, code)
+		}
 	}
+
+	// Deduplicate and save back companyCodes
+	var uniqueCodes []string
+	seenCodes := map[string]bool{}
+	for _, c := range existingCodes {
+		if !seenCodes[c] && c != "" {
+			seenCodes[c] = true
+			uniqueCodes = append(uniqueCodes, c)
+		}
+	}
+	if len(uniqueCodes) > 0 {
+		traits["companyCodes"] = uniqueCodes
+	}
+
 	if req.Department != nil {
 		traits["department"] = strings.TrimSpace(*req.Department)
 	}
@@ -1420,16 +1465,32 @@ func (h *UserHandler) UpdateUser(c *fiber.Ctx) error {
 				}
 			}
 
-			// [Self-Healing] If the UI explicitly assigned the tenant, force a Keto relation sync.
-			// This fixes issues where local DB had the tenant, but Keto failed to create the relation previously.
-			if req.CompanyCode != nil && h.KetoOutboxRepo != nil && updatedLocalUser.TenantID != nil {
-				_ = h.KetoOutboxRepo.Create(bgCtx, &domain.KetoOutbox{
-					Namespace: "Tenant",
-					Object:    *updatedLocalUser.TenantID,
-					Relation:  "members",
-					Subject:   "User:" + updatedLocalUser.ID,
-					Action:    domain.KetoOutboxActionCreate,
-				})
+			// [Self-Healing] Sync all companyCodes to Keto
+			if h.KetoOutboxRepo != nil && h.TenantService != nil {
+				if codes, ok := updated.Traits["companyCodes"].([]interface{}); ok {
+					for _, cVal := range codes {
+						if cStr, ok := cVal.(string); ok && cStr != "" {
+							if tenant, err := h.TenantService.GetTenantBySlug(bgCtx, cStr); err == nil && tenant != nil {
+								_ = h.KetoOutboxRepo.Create(bgCtx, &domain.KetoOutbox{
+									Namespace: "Tenant",
+									Object:    tenant.ID,
+									Relation:  "members",
+									Subject:   "User:" + updatedLocalUser.ID,
+									Action:    domain.KetoOutboxActionCreate,
+								})
+							}
+						}
+					}
+				} else if updatedLocalUser.TenantID != nil {
+					// Fallback if companyCodes doesn't exist
+					_ = h.KetoOutboxRepo.Create(bgCtx, &domain.KetoOutbox{
+						Namespace: "Tenant",
+						Object:    *updatedLocalUser.TenantID,
+						Relation:  "members",
+						Subject:   "User:" + updatedLocalUser.ID,
+						Action:    domain.KetoOutboxActionCreate,
+					})
+				}
 			}
 		}()
 	}