Add OEVG nameplate appearance options

Match ShaguTweaks border themes, add modern health and cast textures, and make the level number adjustable. Keep target color on the border and use a dark masked level inset.

modules/fullalpha.lua

@@ -651,6 +651,7 @@ local function ApplyTargetBorderColor(plate)
       border:SetTexture(wantedTexture)
     end
     plate.BNPTargetBorderTexture = wantedTexture
+    BNP:UpdateLevelBackground(plate)
 
     local needsColor = true
     if border.GetVertexColor then
@@ -978,6 +979,7 @@ local function InstallAlphaGuard(plate)
     -- reintroduce a visible grey/red flash on tagged mobs. The expensive owner
     -- query inside ApplyForeignTagVisual is already cached to 10 Hz.
     ApplyForeignTagVisual(current)
+    BNP:UpdateLevelBackground(current)
 
     -- Native projection can reset the raid icon anchor on any frame. Correct
     -- visible marks before rendering; the Y-offset loop leaves their anchors