loadSpellVisualDbc() now builds two distinct maps:
spellVisualCastPath_ — visualId → M2 via SpellVisual.CastKit chain
spellVisualImpactPath_ — visualId → M2 via SpellVisual.ImpactKit chain
playSpellVisual() accepts useImpactKit=false (default, cast) / true (impact).
SMSG_PLAY_SPELL_IMPACT passes useImpactKit=true so impact effects (explosions,
debuff indicators) use the ImpactKit model instead of the CastKit model.
Added ImpactKit field to all four dbc_layouts.json files.