SAMs ignore allied MIRV warheads that can destroy nearby buildings

A MIRV aimed at one player can destroy a neighboring ally’s buildings through splash damage. The neighbor’s SAMs ignore the warheads because their launcher is friendly.

Ultimus_Rex reported losing a large factory stack this way: [Discord report](https://discord.com/channels/1359946986937258015/1522502120107016283).

To reproduce, ally with the MIRV launcher, place a building near the target player’s border, and cover it with a SAM that can intercept the incoming warhead. A nearby warhead can destroy the building without the SAM firing.

SAMs should consider allied MIRV warheads whose blast can reach their owner’s buildings, subject to normal interception range, timing and cooldown. Alliance and betrayal rules should stay unchanged.

I have a fix and regression tests ready. Could this be approved and assigned to me?

Discord: komyak

Start by reproducing the scenario with an allied MIRV launcher, a nearby building, and a covering SAM, then trace the SAM interception logic and MIRV warhead splash handling. Add or inspect regression tests for allied warhead interception; done means an in-range SAM can intercept a threatening allied warhead without changing alliance or betrayal rules.

Written by the indexing model from the issue text.