I can't even understand how supernovae emit like "more energy than than the sun over it's entire lifetime"

Just... how? I get what happens with fusion but the numbers are so mind boggling. And it makes what seems like a terrifying ball of fire appear as a space heater in comparison. It's nuts. The GW thing you mention is near incomprehensible to me.

One of the rather curious facts about the Sun is that its net energy emissions, on a unit-mass basis, are roughly the same as a mammalian metabolism.

That is, your body is converting mass to energy (the only way the conversion is possible) through chemical processes (ATP-mediated molecular breakdown in the Krebs cycle) at roughly the same rate that the Sun is converting mass to energy through fusion of hydrogen to helium (modulo some pathway hand-waving).

You'll need far more input chemical fuel (carbohydrates and fats, mostly) than the Sun needs of input hydrogen fuel. But the net energy release rate is roughly equivalent.

The biggest difference between you and the Sun is that it (presumably) weighs somewhat more than you do. So that per-unit-mass conversion is multiplied by a much greater mass.

At this scale it can help to think in terms of mass rather than energy. The most energy the sun could ever emit over its lifetime is if it was completely converted into energy. However, this merger emitted 15 times the mass of the sun as energy. I don't have all the numbers on tap for supernovas but given that the sun won't convert all its mass to energy, it's not hard for a supernova to convert more mass in its explosion into energy than the sun ever will.

You mean "every single star in the universe", right?

In the visible universe. The universe may well be infinite.

Observable universe. Dark matter does not emit light.