Against that, you're probably going to need a Botnet or Hive golem (maybe a Cursed golem can make an appreciable dent), or suicide bomb a couple Martyrs into that. Alternately, Mk3 EMP the planet and let your fleet go nuts. If all that fails, nuke it from orbit. 50 AIP is a pretty small price to pay compared to 13k mk4 bombers. 13k mk4 bombers is something I certainly would never want to see.
On defense, set up a network of mk3 grav turrets plus a military mk3 command station (unless you already have Spire starships unlocked for the muniboost). You're going to want to give yourself as much time to kill the bombers as quickly as possible. If you've been saving up a cap of mercenary mk4 fighters, now would be the time to use them (Mercenary Etherjets and Beam Frigates as well if you have the resources). A trio of mk2 Riot controls with Tazers may be able to do something, not sure, and if you have the time/resources (again, always an issue), see if you can set up all your lightning turrets (mk2 and mk3 included) on that wormhole to try to deal as much damage as possible while they're gravved.
