feat(devices): add console-only display name (console_name)

Lets staff set a friendly name for a device independent of whatever
name the end user gave it in the app. console_name is never shown to
app users and never synced from/to device_name; every display label
across search, equipment/helpdesk name resolution, device search, and
the Manage tab's issue linker now falls back through console_name ->
device_name -> serial rather than device_name alone.

Also includes an incidental one-line fix in devices/service.py: the
nested-struct deep-merge in update_device() was missing the newly
added device_health_settings key.

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

backend/search/router.py

@@ -26,8 +26,9 @@ def _search_devices(q: str) -> list[dict]:
         return []
     out = []
     for d in results[:LIMIT]:
-        label = d.device_name or d.serial_number or d.device_id or d.id
-        sublabel = d.serial_number if d.device_name else None
+        display_name = d.console_name or d.device_name
+        label = display_name or d.serial_number or d.device_id or d.id
+        sublabel = d.serial_number if display_name else None
         out.append({
             "type": "device",
             "id": d.id,