Number of active websites hosted on AEWEB

### Is your feature request related to a problem?

I would like to get the number of chains in the BC with a not empty hosting reference transaction in the last tx of each chain
The goal is to display on AEWEB App the number of active website on AEWEB

### Describe the solution you'd like

_No response_

### Additional context

_No response_

Start by locating the Elixir code that reads transaction chains and exposes data to AEWEB App, then inspect how the last transaction and hosting reference are represented. Define the count as chains whose latest transaction has a non-empty hosting reference, and verify that the resulting value is available for display in AEWEB App.

Written by the indexing model from the issue text.