Add the dualpath-as-single-machine site toggle

Most facilities consider a Dualpath pair one physical dual-bay machine.
New site setting dualpath_single_machine (default on): the machines
list, dashboard counts, machines-by-type report, and floor map collapse
each pair to its primary bay (lower assetnumber), with combined
2007 / 2008 labels; pagination totals stay honest. Detail pages remain
per-bay and always show a dual-bay sibling banner linking the partner.
Pair resolution lives in core services and joins the plugin contract
surface (0.8.0 -> 0.9.0).

On the WJ dataset: 31 pairs collapse, machine counts 262 -> 231, map
470 assets. Toggle verified live in both states, left on.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

frontend/src/views/machines/MachineDetail.vue

@@ -16,6 +16,16 @@
     <div v-if="loading" class="loading">Loading...</div>
 
     <template v-else-if="machine">
+      <!-- Dual-bay sibling banner: a Dualpath pair is one physical machine -->
+      <div v-if="machine.dualpathpartner" class="dualpath-banner">
+        Dual-bay machine - sibling bay:
+        <router-link
+          v-if="machine.dualpathpartner.machineid"
+          :to="`/machines/${machine.dualpathpartner.machineid}`"
+        >{{ machine.dualpathpartner.assetnumber }}</router-link>
+        <span v-else>{{ machine.dualpathpartner.assetnumber }}</span>
+      </div>
+
       <!-- Hero Section -->
       <div class="hero-card">
         <div class="hero-content">
@@ -264,6 +274,22 @@ function formatDate(dateStr) {
   font-family: 'SF Mono', 'Monaco', 'Consolas', monospace;
 }
 
+.dualpath-banner {
+  margin-bottom: 16px;
+  padding: 10px 14px;
+  border-radius: 6px;
+  background: var(--bg-card);
+  border: 1px solid var(--border);
+  border-left: 4px solid var(--primary);
+  color: var(--text);
+  font-size: 0.9rem;
+}
+
+.dualpath-banner a {
+  color: var(--link);
+  font-weight: 600;
+}
+
 .feature-tag {
   display: inline-block;
   padding: 0.3rem 0.625rem;