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
 

docs/PLUGIN-HOOKS.md

@@ -9,7 +9,7 @@ The contract is locked in [ADR-001](../docs/adr/ADR-001-asset-as-platform-contra
 The framework declares its contract version in `shopdb/__init__.py`:
 
 ```python
-__contract_version__ = '0.8.0'
+__contract_version__ = '0.9.0'
 ```
 
 Each plugin's `manifest.json` declares the range of contract versions it supports:
@@ -429,7 +429,8 @@ What `shopdb.api` exposes:
   `ErrorCodes`
 - Pagination: `get_pagination_params`, `paginate_query`
 - Authorization: `require_permission`, `require_role`
-- Helpers: `audit_log`, `resolve_asset_position`
+- Helpers: `audit_log`, `resolve_asset_position`, `resolve_dualpath_pairs`,
+  `dualpath_single_machine_enabled`
 - Import mode: `apply_import_timestamps`, `import_mode_active`,
   `parse_import_datetime`
 - Legacy employee directory: `employee_connection`
@@ -482,6 +483,31 @@ position = resolve_asset_position(asset)
 
 See [ADR-001](../docs/adr/ADR-001-asset-as-platform-contract.md) for the position resolution algorithm.
 
+### Dualpath single-machine collapse
+
+A Dualpath relationship pair is one physical dual-bay machine recorded as two
+asset rows. When the site setting `dualpath_single_machine` is on (default), the
+machines list, dashboard/report counts, and the floor map show the pair as a
+single machine (the SECONDARY bay is hidden); the data model always keeps both
+rows and detail pages stay per-bay.
+
+```python
+from shopdb.api import resolve_dualpath_pairs, dualpath_single_machine_enabled
+
+collapse = resolve_dualpath_pairs()
+# collapse.secondaryassetids: set of the non-primary bay asset ids to hide
+# collapse.partnerbyasset: {assetid -> {'assetid', 'assetnumber'}} for every
+#                          pair member (primary and secondary), for banners
+
+if dualpath_single_machine_enabled():
+    # exclude the hidden bays and annotate the visible (primary) bay
+    ...
+```
+
+PRIMARY is the pair member with the lower natural-sort assetnumber.
+`resolve_dualpath_pairs` ignores the toggle (so a detail-page sibling banner can
+show always); gate the collapse itself on `dualpath_single_machine_enabled()`.
+
 ### Import mode (legacy timestamp passthrough)
 
 Bulk imports from the classic ASP shopdb need to preserve each row's original