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/helpdesk/service.py

@@ -50,7 +50,8 @@ def _resolve_device_name(db, device_id: str) -> str:
     try:
         doc = db.collection("devices").document(device_id.strip()).get()
         if doc.exists:
-            return doc.to_dict().get("device_name", "")
+            data = doc.to_dict()
+            return data.get("console_name") or data.get("device_name", "")
     except Exception as e:
         print(f"[helpdesk] Error resolving device name: {e}")
     return ""