Use nullish coalescing operator (S6606) and fix duplicate id (S7930)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/components/AppHeader.vue

@@ -8,8 +8,8 @@
         class="flex justify-between items-center relative"
         v-show="showMember"
       >
+        <span id="acct_mgmt_button">
           <img
-          id="acct_mgmt_button"
             v-if="!isHeadHovered"
             src="@/assets/icon-head-black.svg"
             @mouseenter="isHeadHovered = true"
@@ -20,7 +20,6 @@
             alt="user-head"
           />
           <img
-          id="acct_mgmt_button"
             v-else
             src="@/assets/icon-head-blue.svg"
             @mouseleave="isHeadHovered = false"
@@ -30,6 +29,7 @@
             class="cursor-pointer z-50"
           alt="user-head"
           />
+        </span>
       </div>
     </div>
   </div>

src/stores/acctMgmt.ts

@@ -184,7 +184,7 @@ export const useAcctMgmtStore = defineStore('acctMgmtStore', {
 
       try {
         const response = await apiClient.put(apiEdit, {
-          username: editDetail.newUsername != null ? editDetail.newUsername : editDetail.username,
+          username: editDetail.newUsername ?? editDetail.username,
           password: editDetail.password,
           name: editDetail.name,
           is_active: editDetail.is_active,