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/devices/service.py

@@ -159,9 +159,10 @@ def list_devices(
         if search:
             search_lower = search.lower()
             name_match = search_lower in (device.device_name or "").lower()
+            console_name_match = search_lower in (device.console_name or "").lower()
             location_match = search_lower in (device.device_location or "").lower()
             sn_match = search_lower in (device.serial_number or "").lower()
-            if not (name_match or location_match or sn_match):
+            if not (name_match or console_name_match or location_match or sn_match):
                 continue
 
         results.append(device)
@@ -222,7 +223,7 @@ def update_device(device_doc_id: str, data: DeviceUpdate) -> DeviceInDB:
     # Deep-merge nested structs so unmentioned sub-fields are preserved
     existing = doc.to_dict()
     nested_keys = (
-        "device_attributes", "device_subscription", "device_stats",
+        "device_attributes", "device_subscription", "device_stats", "device_health_settings",
     )
     for key in nested_keys:
         if key in update_data and isinstance(existing.get(key), dict):