Phase 0: scaffold Gradle multi-project mod skeleton

common/ (shared source) plus three leaf modules: forge-1_12_2 (primary,
Enigmatica 2 target) and forge-1_7_10 both build via anatawa12's
Gradle-7-compatible ForgeGradle 1.2/2.3 forks (verified: both leaves build
clean on Gradle 7.6 / JDK 8). neoforge-26_1 is structurally scaffolded but
excluded from the default build pending its own toolchain in Phase 10.

settings.gradle

@@ -0,0 +1,24 @@
+pluginManagement {
+    repositories {
+        gradlePluginPortal()
+        maven { url = 'https://maven.minecraftforge.net/' }
+        maven { url = 'https://maven.neoforged.net/releases' }
+        mavenCentral()
+    }
+}
+
+rootProject.name = 'mcmapper-mod'
+
+// `common` is not a buildable Gradle subproject — it's shared source, pulled directly into
+// each leaf's own source set (see common/README.md for why).
+include 'forge-1_7_10'
+include 'forge-1_12_2'
+
+// neoforge-26_1 is intentionally NOT included in the default build: both legacy leaves
+// (forge-1_7_10, forge-1_12_2) use anatawa12's ForgeGradle 1.2/2.3 forks, which need Gradle 7.6
+// and JDK 8 (see gradle.properties' org.gradle.java.home pin and this project's
+// gradle-wrapper.properties). ModDevGradle (used by neoforge-26_1) needs Gradle 8+ and JDK 17+
+// to even apply the plugin — incompatible with that daemon within one invocation. Until Phase 10
+// gives it a proper isolated build setup, it can only be built by pointing org.gradle.java.home
+// at a JDK 21+ install and invoking Gradle (8+) from inside the neoforge-26_1/ directory
+// directly, with its own wrapper. The module itself is fully scaffolded and ready.