Chained mod target overlays

- Mod targets list an ordered overlay chain; later overlays replace earlier ones and earlier source replacements apply to inherited files
- Forge and NeoForge metadata take their loader version range from the target
- The Fabric permissions library is bundled only for targets that declare it
- Dropped the 1.21.1 mods.toml copies that only differed in the loader range

adapters/neoforge/src/main/resources/META-INF/neoforge.mods.toml

@@ -25,7 +25,7 @@ logoFile = "assets/irisworldgen/icon.png"
 [[dependencies.irisworldgen]]
 modId = "neoforge"
 type = "required"
-versionRange = "[26.3.0.65-beta,26.4)"
+versionRange = "${loaderRange}"
 ordering = "NONE"
 side = "BOTH"