Farlands Tweaks Core 1.3 - CustomNPCsJEICompat1

Compatibility target:
- CustomNPCs 1.20.1.20260711
- JEI 15.59.0.212

CustomNPCs MixinJEIEventHandler expects:
  onDrawBackgroundPost(Screen, GuiGraphics)

JEI 15.59.0.212 provides:
  onDrawBackgroundPost(GuiGraphics)

The coremod verifies the exact known CustomNPCs handler descriptor and bytecode,
then changes only that handler to the JEI 15.59 callback signature. Its Screen
test is preserved by reading Minecraft.getInstance().screen. The other two
CustomNPCs JEI handlers and every other CustomNPCs mixin remain unchanged.

The internal Farlands Tweaks version remains 1.3 for MATCH_VERSION compatibility.
