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/PCDetail.vue

@@ -15,7 +15,7 @@
       <div class="hero-card">
         <div class="hero-content">
           <div class="hero-title">
-            <h1>{{ computer.assetnumber }}</h1>
+            <h1>{{ computer.computer?.hostname || computer.serialnumber || computer.assetnumber }}</h1>
             <span v-if="identifierflags.fqdn && computer.computer?.hostname" class="hero-alias">{{ computer.computer.hostname }}</span>
           </div>
           <div class="hero-meta">