fix: TBC Anniversary patch 2.5.6 (Interface 20506) compatibility

[kyleian]

Problem

TBC Anniversary patch 2.5.6 (Interface 20506) removed the DebuffTypeColor global table and replaced it with individual DEBUFF_TYPE_*_COLOR constants. Any reference to DebuffTypeColor now returns nil, which causes the following error on every FullUpdate call:

auras.lua:562: attempt to index global 'DebuffTypeColor' (a nil value)

This aborts the entire unit frame update, leaving target frames with no names, no bars, and no buffs/debuffs shown.

Solution

Reconstruct DebuffTypeColor from the new per-school constants in ExternalAPI.lua (which is loaded first per the TOC), guarded by if not DebuffTypeColor then so the shim is a no-op on older client versions that still provide the global.

Keys reconstructed:

• .none / [""] — fallback used in auras.lua and highlight.lua
• "Magic", "Curse", "Disease", "Poison" — school types returned by UnitAura

Both TOC files also add 20506 to the ## Interface list so the client loads the addon without an out-of-date warning.

Files changed

File	Change
ExternalAPI.lua	Add DebuffTypeColor compat shim (guarded by if not DebuffTypeColor)
ShadowedUnitFrames.toc	Add 20506 to ## Interface list
options/ShadowedUF_Options.toc	Add 20506 to ## Interface list

Testing

Tested on TBC Anniversary build 68575 (Interface 20506) — debuff colors, aura display, and unit frame names all work correctly after this patch.

[kyleian]

Closing in favor of #74, which takes the correct approach.

#74 adds ShadowUF.API.GetDebuffTypeColor() as a namespaced helper rather than reconstructing DebuffTypeColor as a global, updates all three actual call sites (auras.lua, health.lua, highlight.lua), handles Bleed which this PR missed, and passes the repository luacheck configuration with 0 warnings. The global-reconstruction approach here is also fragile — a future patch could remove additional globals and the pattern would have to be repeated.

#74 is the better fix.