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>

docs/CONFIG.md

@@ -135,6 +135,7 @@ read back through the API.
 | `pc_access_domain` | `device.geaerospace.net` | Domain appended to a PC hostname for remote-access links. Blank = hostname as-is. |
 | `employeeid_pattern` | `^\d{9}$` | Regex a search term must match to be treated as an employee id. Invalid regex falls back to the default and never 500s. |
 | `printer_hostname_template` | `Printer-{ip}.printer.geaerospace.net` | Printer hostname template. `{ip}` is the dash-separated IP address. |
+| `dualpath_single_machine` | `true` | Treat a Dualpath pair (a dual-bay machine with one controller) as a single machine in the machines list, dashboard/report counts, and the floor map (the secondary bay is hidden). The data model always keeps both bay records; detail pages stay per-bay with a sibling banner. `false` lists and counts both bays separately. |
 
 ### branding