Unable to change the server of an existing template widget

**Home Assistant Android app version(s):** 2025.11.4-full (19134)

**Android version(s):** 11

**Device model(s):** Samsung Galaxy A40

**Home Assistant version:** 2025.11.5

**Description of problem, include YAML if issue is related to notifications:**
When changing the server of an existing template widget, the **UPDATE WIDGET** button becomes inactive. No action will return this button to its active state. You can only exit without saving.

**Screenshot or video of problem:**
Edit an existing widget. Button is active:

Change server:

The button becomes inactive. And error message appears.

Change template code:

The button still inactive and the same error message is here.

Start by reproducing the existing template widget edit flow on the reported Android and Home Assistant versions, focusing on changing the selected server. Trace the validation that controls the UPDATE WIDGET button and compare it with editing the template code. Done means changing the server leaves the button active and the updated widget can be saved.

Written by the indexing model from the issue text.