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.

gradle.properties

@@ -0,0 +1,25 @@
+org.gradle.jvmargs=-Xmx3G
+org.gradle.daemon=false
+
+# forge-1_12_2 and forge-1_7_10 (legacy ForgeGradle 1.2/2.3, see their build.gradle + this repo's
+# README) need the Gradle daemon itself running on JDK 8 — newer JDKs aren't supported by that
+# tooling. Point org.gradle.java.home at a JDK 8 install, either via a JAVA_HOME env var or by
+# adding org.gradle.java.home=/path/to/jdk-8 to a local, untracked override (see local.properties
+# in .gitignore — Gradle also honours a gradle.properties in $GRADLE_USER_HOME for this without
+# touching this tracked file at all).
+
+mod_version=0.1.0-SNAPSHOT
+mod_id=mcmapper
+
+# forge-1_7_10
+minecraft_1_7_10_version=1.7.10
+forge_1_7_10_version=10.13.4.1614-1.7.10
+
+# forge-1_12_2
+minecraft_1_12_2_version=1.12.2
+forge_1_12_2_version=14.23.5.2847
+mcp_1_12_2_mappings=stable_39
+
+# neoforge-26_1 (loader assumed NeoForge — confirm before Phase 10, see plan's Open Assumptions)
+minecraft_26_1_version=26.1.2
+neoforge_26_1_version=26.1.2