fix: update default values in service form and enhance validation for required fields

apps/dashboard/modules/services/service-form.tsx

@@ -43,10 +43,10 @@ export type ServiceFormProps = {
 // ── Default values ──
 
 const DEFAULT_VALUES: ServiceFormValues = {
-    shop_type: null,
-    category: null,
-    unit_type: null,
-    department: null,
+    shop_type: { value: "", label: "" },
+    category: { value: "", label: "" },
+    unit_type: { value: "", label: "" },
+    department: { value: "", label: "" },
     labor_name: "",
     service_code: "",
     labor_matrix: "",

apps/dashboard/modules/services/service.schema.ts

@@ -5,8 +5,13 @@ export const relationFieldSchema = z
     .object({ value: z.string(), label: z.string() })
     .nullable()
 
-const requiredRelationFieldSchema = relationFieldSchema.refine((value) => value !== null, {
-    message: "This field is required",
+const requiredRelationFieldSchema = relationFieldSchema.superRefine((value, ctx) => {
+    if (!value?.value) {
+        ctx.addIssue({
+            code: z.ZodIssueCode.custom,
+            message: "This field is required",
+        })
+    }
 })
 
 const optionalNumericField = z.preprocess(