Prioritize Splinter Weapon targets

[Wellwisher533]

Summary

• give Splinter Weapon a dedicated target policy
• prioritize the martial caster, then martial party members, Ebon Vanguard Assassin, and finally minions
• skip dead, untargetable, out-of-range, or already weapon-spelled candidates so fallback continues
• use the same selector in regular HeroAI, BuildMgr/headless, and legacy SkillManager

Verification

• all six changed Python files compile
• 9 focused local targeting and wiring tests pass (test file intentionally not submitted)
• confirmed working in-game by the user

Notes

• generic AllyMartial targeting is unchanged
• target enum value 44 leaves value 43 available for the open Ancestors' Rage targeting PR (Target Ancestors' Rage by adjacent enemy density #91)