Add support for Add to watch favorite

[TimoPtr]

We've introduced Add to feature in https://github.com/home-assistant/android/pull/5622 and it would be nice to extend it to Watch favorite.

The UI for selecting an action is available starting from HA core 2025.12.0 or (in nightly/dev).

• we need to adjust the logic of EntityAddToHandler to only display the watch option if a watch is available (disconnected or not)
• The option should only be enabled when the watch is connected.

In this task you will also have to update the unit tests in EntityAddToHandlerTest

[dshokouhi]

We actually don't support multiple watches but only the first connected one

[TimoPtr]

We actually don't support multiple watches but only the first connected one

I updated the description.

[ujjol1234]

@TimoPtr can I work on this?

[TimoPtr]

@TimoPtr can I work on this?

Not yet. The frontend part is not yet done.

[ujjol1234]

No worries, I will look for some other issues to work on.

[TimoPtr]

This can be worked on since the PR on the frontend and android have been merged.

[jpelgrom]

Related issue which will also apply here: #6038