fix(ldap): remove DTO default initializers that clobbered partial updates

CreateLdapConfigDto's optional fields (searchFilter, syncIntervalMin,
isActive, groupFilterDns) had class-field default initializers.
NestJS's ValidationPipe instantiates DTOs via plainToInstance, which
applies those defaults even when the field is absent from the request
body -- so any partial PATCH not including a given field silently
reset it to the hardcoded default instead of leaving it untouched.

Caught by testing the new groupFilterDns-only PATCH: saving the group
filter alone reset searchFilter back to "(objectClass=person)",
clobbering the configured Active Directory filter. The service layer
already has its own `?? default` fallback for create, so the DTO
initializers were redundant and unsafe. Removing them makes updateConfig's
existing "only set if dto.field !== undefined" pattern behave correctly
for every optional field, not just the ones sent together in one request.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

apps/api/src/ldap/dto/ldap-config.dto.ts

@@ -31,21 +31,21 @@ export class CreateLdapConfigDto {
 
   @IsString()
   @IsOptional()
-  searchFilter?: string = '(objectClass=person)';
+  searchFilter?: string;
 
   @IsInt()
   @IsOptional()
   @Min(0)
-  syncIntervalMin?: number = 60;
+  syncIntervalMin?: number;
 
   @IsBoolean()
   @IsOptional()
-  isActive?: boolean = true;
+  isActive?: boolean;
 
   @IsArray()
   @IsString({ each: true })
   @IsOptional()
-  groupFilterDns?: string[] = [];
+  groupFilterDns?: string[];
 }
 
 /**