## Summary
A meer mage fights `FightMode.Evil` and its enraged creatures carry -1000 karma, so `BaseCreature.IsEnemy` made each an enemy of the other:
- The meer acquired its own enraged creatures as ordinary targets.
- An enraged creature fell back to attacking its meer when nothing else was in range. It isn't `Summoned`, so it reached the meer through `AcquireNewFocusMob`'s summon-master fallback.
`BaseEnraged` and `MeerMage` now override `IsEnemy` to exclude each other. Another meer's creatures stay enemies.
`BaseEnraged` also pulled its meer into fights against any creature with a `SummonMaster`, which included another meer's enraged creatures. It now checks `GetMaster()`, matching the "controlled/summoned" OSI note in that method.
## Test plan
- [x] `MeerAndItsEnragedCreature_AreNotEnemies`: fails before the fix
- [x] `AnotherMeersEnragedCreature_StaysAnEnemy`
- [x] `MeerAndItsEnragedCreature_NeverAcquireEachOther`: fails before the fix (the meer acquired its own creature)
- [x] UOContent.Tests (1171 passed, 2 skipped) and Server.Tests (907) green
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