PCs: identify by hostname/serial, drop the PC Number field

PCs are identified by hostname (the primary identifier) with serial as the
fallback; the assetnumber is seeded from hostname rather than a separate
"PC Number" field. PC list shows Hostname/Serial (Asset Tag column removed),
PC detail title leads with hostname.

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

frontend/src/views/pcs/PCsList.vue

@@ -24,7 +24,6 @@
           <table>
             <thead>
               <tr>
-                <th>Asset Tag</th>
                 <th>Hostname</th>
                 <th>Serial Number</th>
                 <th>Type</th>
@@ -36,7 +35,6 @@
             </thead>
             <tbody>
               <tr v-for="item in computers" :key="item.assetid">
-                <td>{{ item.assetnumber }}</td>
                 <td>{{ item.computer?.hostname || '-' }}</td>
                 <td class="mono">{{ item.serialnumber || '-' }}</td>
                 <td>{{ item.computer?.computertypename || '-' }}</td>
@@ -61,7 +59,7 @@
                 </td>
               </tr>
               <tr v-if="computers.length === 0">
-                <td colspan="8" style="text-align: center; color: var(--text-light);">
+                <td colspan="7" style="text-align: center; color: var(--text-light);">
                   No computers found
                 </td>
               </tr>