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.

README.md

@@ -0,0 +1,48 @@
+# MCMapper-Mod
+
+Thin, version-independent Forge/NeoForge client for [MCMapper-Backend](https://git.octoturge.com/octoturge/MCMapper-Backend).
+Streams delta block updates out to the backend instead of rendering the map on the MC server
+itself (the Bluemap/Dynmap resource problem this project exists to avoid). Full architecture
+and phased delivery plan lives in the backend repo's planning docs / was tracked during design
+in Claude Code's plan mode.
+
+## Repo layout
+
+- `common/` — loader-agnostic Java: protocol types, config model, and the interfaces
+  (`ChunkAdapter`, `ChatBridge`, `BackendConnection`) each leaf implements. Not a compiled
+  dependency — pulled in as source per leaf (see `common/README.md`).
+- `forge-1_12_2/` — **primary leaf**, MC 1.12.2 Forge. First implemented; this is the actual
+  driving use case (an Enigmatica 2 modpack server). Builds with legacy ForgeGradle 2.3 via
+  anatawa12's Gradle-7-compatible fork (see `THIRD_PARTY_NOTICES.md`).
+- `forge-1_7_10/` — MC 1.7.10 Forge. Second priority. Builds with legacy ForgeGradle 1.2, same
+  fork family, one Forge-tooling generation further back.
+- `neoforge-26_1/` — MC 26.1.2 (NeoForge, assumed). Lowest MVP priority. Structurally scaffolded,
+  not yet wired into the default build (see `settings.gradle`).
+
+## Version targets and priority
+
+1. **MC 1.12.2 Forge** — highest priority (Enigmatica 2)
+2. **MC 1.7.10 Forge** — also a priority
+3. **MC 26.1.2** — lowest of the three MVP targets
+
+Fabric support is an explicit future phase, not part of the MVP.
+
+## Building
+
+Both legacy leaves share one root build, on Gradle 7.6 / JDK 8 (pinned via
+`org.gradle.java.home` in `gradle.properties` — see `settings.gradle` for why):
+
+```
+./gradlew :forge-1_12_2:build
+./gradlew :forge-1_7_10:build
+```
+
+The first build downloads Minecraft/Forge artifacts and MCP mappings from Forge's Maven and can
+take a while / needs network access. `neoforge-26_1` is not yet buildable from the root — it
+needs Gradle 8+ and JDK 17+ (ModDevGradle), incompatible with the legacy leaves' toolchain
+within one Gradle invocation; see `settings.gradle`'s comment for the workaround until Phase 10
+gives it a proper isolated build.
+
+## Attribution
+
+See `THIRD_PARTY_NOTICES.md`.