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/MachinesList.vue

@@ -36,7 +36,9 @@
             </thead>
             <tbody>
               <tr v-for="item in machines" :key="item.assetid">
-                <td>{{ item.assetnumber }}</td>
+                <td>
+                  {{ item.assetnumber }}<template v-if="item.dualpathpartner"> / {{ item.dualpathpartner.assetnumber }}</template>
+                </td>
                 <td>{{ item.name || '-' }}</td>
                 <td class="mono">{{ item.serialnumber || '-' }}</td>
                 <td>{{ item.machine?.machinetypename || '-' }}</td>