fix(backoffice): make position type optional for unit departments

Creating a department under a unit required picking a position type,
which is not always known at that point. Sub-department creation is
unchanged and still requires one.

PositionPayload.positionTypeId becomes optional and the field is omitted
from the request body when unset rather than sent as an empty string.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

apps/edr-freight-web/backoffice/src/user-management/services/api/positionService.ts

@@ -21,7 +21,7 @@ export interface PositionPayload {
   organizationId: string;
   parentPositionId?: string;
   projectId?: string;
-  positionTypeId: string;
+  positionTypeId?: string;
 }
 export interface PositionQueryParams {
   orderBy?: string;

apps/edr-freight-web/backoffice/src/user-management/userManagement/forms/AddDepartmentForm.tsx

@@ -48,8 +48,6 @@ export function AddDepartmentForm({
     if (!nameAm.trim())
       newErrors.nameAm = t("organization.amharicNameRequired");
     if (!key.trim()) newErrors.key = t("contentManagement.keyRequired");
-    if (!positionTypeId)
-      newErrors.positionTypeId = t("contentManagement.selectPosType");
 
     setErrors(newErrors);
     return Object.keys(newErrors).length === 0;
@@ -71,7 +69,7 @@ export function AddDepartmentForm({
       key: key.trim().toLowerCase().replace(/\s+/g, "-"),
       unitId,
       organizationId,
-      positionTypeId,
+      ...(positionTypeId ? { positionTypeId } : {}),
     };
 
     createPosition({
@@ -90,12 +88,11 @@ export function AddDepartmentForm({
   return (
     <form onSubmit={handleSubmit} className="space-y-4">
       <div className="space-y-2">
-        <Label htmlFor="positionType">{t("organization.positionTypes")}</Label>
+        <Label htmlFor="positionType">
+          {t("organization.positionTypes")} ({t("common.optional")})
+        </Label>
         <Select
-          onValueChange={(value) => {
-            setPositionTypeId(value);
-            setErrors((prev) => ({ ...prev, positionTypeId: "" }));
-          }}
+          onValueChange={setPositionTypeId}
           value={positionTypeId}
           disabled={isLoadingTypes}
         >
@@ -110,9 +107,6 @@ export function AddDepartmentForm({
             ))}
           </SelectContent>
         </Select>
-        {errors.positionTypeId && (
-          <p className="text-red-500 text-sm">{errors.positionTypeId}</p>
-        )}
       </div>
 
       <div className="space-y-2">