Add authentication and validation to delete-interest API, refactor modal list item

- Add x-tag header authentication check to delete-interest endpoint
- Add ID validation and improved error handling with proper typing
- Refactor InterestDetailsModal v-select item template structure

components/InterestDetailsModal.vue

@@ -389,15 +389,18 @@
                     <template v-slot:item="{ item, props }">
                       <v-list-item 
                         v-bind="props"
+                        :title="item.value"
                       >
                         <template v-slot:prepend>
                           <v-icon :color="getSalesLevelColor(item.value)">
                             mdi-circle
                           </v-icon>
                         </template>
-                        <v-list-item-title :style="{ color: getSalesLevelColor(item.value) }">
-                          {{ item.value }}
-                        </v-list-item-title>
+                        <template v-slot:title>
+                          <span :style="{ color: getSalesLevelColor(item.value) }">
+                            {{ item.value }}
+                          </span>
+                        </template>
                       </v-list-item>
                     </template>
                   </v-select>