[FR] Provide an API to transfer large amount of data on Wifi between phone and watch when possible.

Following a discussion on Slack. It would be nice to have an high level API that allows watch to get large data from the phone but using Wifi when both the watch and the phone can be connected to the same network.

Typical use case would be to download music from the phone to the watch to play without the phone available. There's still people storing their music on sdcards or on servers that can't transcode to smaller file and need to sync via the phone.

A first step would be to have an API allowing to check that both devices are connected to the same wifi network and can communicate.

Then if possible build a transfer solution on top of that.

My naive way if I was to do it, would be the watch ask the phone to open a socket on a port (returns error if phone not on wifi or actual error or return the wifi ip and port). The watch check if it can connect to wifi, connect then try to connect to that socket with a well known message.

Start with the Slack discussion referenced by the issue and review how phone/watch communication currently works in the repository. Define the first milestone as detecting whether both devices share a reachable WiFi network, then evaluate the proposed socket-based transfer for large music files. Done should include an agreed API scope and a tested transfer approach.

Written by the indexing model from the issue text.