PC Number defaults to serial number (editable)

On a new PC, the PC Number (assetnumber) auto-fills from the serial number as
it is typed, but stops auto-filling once the user edits it manually. Edit mode
never auto-overwrites.

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

frontend/src/views/pcs/PCForm.vue

@@ -17,7 +17,9 @@
               type="text"
               class="form-control"
               required
+              @input="onPcNumberInput"
             />
+            <small class="form-hint">Defaults to the serial number; editable</small>
           </div>
 
           <div class="form-group">
@@ -266,7 +268,7 @@
 </template>
 
 <script setup>
-import { ref, onMounted, computed } from 'vue'
+import { ref, onMounted, computed, watch } from 'vue'
 import { useRoute, useRouter } from 'vue-router'
 import { computersApi, assetsApi, vendorsApi, locationsApi, modelsApi, operatingsystemsApi } from '../../api'
 import ShopFloorMap from '../../components/ShopFloorMap.vue'
@@ -281,6 +283,13 @@ const router = useRouter()
 
 const isEdit = computed(() => !!route.params.id)
 
+// PC Number (assetnumber) defaults to the serial number while the user hasn't
+// typed their own. Editable; only auto-fills on a new PC.
+const manualPcNumber = ref(false)
+function onPcNumberInput() {
+  manualPcNumber.value = true
+}
+
 const loading = ref(true)
 const saving = ref(false)
 const error = ref('')
@@ -314,6 +323,13 @@ const models = ref([])
 const locations = ref([])
 const operatingsystems = ref([])
 
+// Default PC Number to serial while the user hasn't typed their own (new PC only)
+watch(() => form.value.serialnumber, (serial) => {
+  if (!isEdit.value && !manualPcNumber.value && serial) {
+    form.value.machinenumber = serial
+  }
+})
+
 // Filter models by selected vendor and PC type
 const filteredModels = computed(() => {
   // filter by vendor only (PC type now maps to computertypeid, a different id