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.

neoforge-26_1/src/main/resources/META-INF/neoforge.mods.toml

@@ -0,0 +1,17 @@
+modLoader = "javafml"
+loaderVersion = "[1,)"
+license = "MIT"
+
+[[mods]]
+modId = "mcmapper"
+version = "${file.jarVersion}"
+displayName = "MCMapper"
+description = "Thin delta-streaming client for the MCMapper web map backend."
+authors = "Octoturge"
+
+[[dependencies.mcmapper]]
+    modId = "neoforge"
+    type = "required"
+    versionRange = "[26.1,)"
+    ordering = "NONE"
+    side = "BOTH"