input: update ctrl+h to toggle `auto-safe` rather than `auto`

It has been odd that ctrl+h toggles `auto` for hwdecs even though we
always recommend people start with `auto-safe`, and `auto` will attempt
various hwdecs that can fail so badly we can't fall back to software
decoding.

With the change to more exhaustively attempt to use hwdecs, it is now
easier to get into situations where these fragile hwdecs will get
attempted in basic scenarios, like pressing ctrl+h.

So it is high time to default to `auto-safe`.