feat(web): clear person birthdate (#18330)

web/src/lib/modals/PersonEditBirthDateModal.svelte

@@ -24,7 +24,7 @@
     try {
       const updatedPerson = await updatePerson({
         id: person.id,
-        personUpdateDto: { birthDate: birthDate.length > 0 ? birthDate : null },
+        personUpdateDto: { birthDate },
       });
 
       notificationController.show({ message: $t('date_of_birth_saved'), type: NotificationType.Info });
@@ -53,6 +53,13 @@
           bind:value={birthDate}
           max={todayFormatted}
         />
+        {#if person.birthDate}
+          <div class="flex justify-end">
+            <Button shape="round" color="secondary" size="small" onclick={() => (birthDate = '')}>
+              {$t('clear')}
+            </Button>
+          </div>
+        {/if}
       </div>
     </form>
   </ModalBody>
@@ -62,8 +69,8 @@
       <Button shape="round" color="secondary" fullWidth onclick={() => onClose()}>
         {$t('cancel')}
       </Button>
-      <Button type="submit" shape="round" color="primary" fullWidth>
-        {$t('set')}
+      <Button type="submit" shape="round" color="primary" fullWidth form="set-birth-date-form">
+        {$t('save')}
       </Button>
     </div>
   </ModalFooter>