Just shipped tip forwarding on posts ...

1. It's hidden in the options pane
2. It's 100% only
3. can only forward to SN users

It's pretty basic support but I'll refine it over time.

All the other schemes are too complicated to start with - sending 1 sat at a time to lightning addresses is not simple. If lots of users end up forwarding, we'll refine it, but I suspect it'll see limited use.