fix(devices): preserve existing URL on PATCH-without-url

When a PATCH omits `url` (rename / icon-only edit), normalized_url
arrived at the processor as None and the manager kept whatever it had
cached — or refused to re-sync if it had nothing. Fall back to
existing.url so the processor is always told the current address.
Surfaced by the production-review backlog.

server/src/ledgrab/api/routes/devices.py

@@ -640,11 +640,18 @@ async def update_device(
             icon_color=update_data.icon_color,
         )
 
-        # Sync connection info in processor manager
+        # Sync connection info in processor manager.
+        #
+        # When a PATCH omits `url` (rename / icon-only edit) `normalized_url`
+        # is None — fall back to the existing record's URL so the processor
+        # is always told the current address, otherwise it silently keeps
+        # whatever it had cached (or worse, treats None as "unconfigured"
+        # and refuses to re-sync).
+        effective_url = normalized_url if normalized_url is not None else existing.url
         try:
             manager.update_device_info(
                 device_id,
-                device_url=normalized_url,
+                device_url=effective_url,
                 led_count=normalized_led_count,
                 baud_rate=update_data.baud_rate,
             )