fix(highlight): manual debuff scan for CoA dispel classes

UnitDebuff(unit, 1, "RAID") ignores CoA custom classes, so on a
Witchdoctor/Templar/etc. hasDebuff was always nil and the unit-frame
border highlight never lit up on curable Poison/Disease/Magic/Curse.

Fix mirrors the auras.lua shim: if ShadowUF.GetCoaDispels() returns a
dispel set, scan UnitDebuff entries manually and match by dispelType.
Expose getCoaDispels on the ShadowUF namespace so highlight.lua can
reuse the single source of truth (COA_CLASS_DISPELS lives in auras.lua).

ShadowedUnitFrames/modules/auras.lua

@@ -40,6 +40,8 @@ local function getCoaDispels()
 	end
 	return playerCoaDispels
 end
+-- Expose for other modules (highlight.lua) so the dispel set stays single-source.
+ShadowUF.GetCoaDispels = getCoaDispels
 local mainHand, offHand = {time = 0}, {time = 0}
 local tempEnchantScan
 ShadowUF:RegisterModule(Auras, "auras", ShadowUF.L["Auras"])