M0' scaffold: Godot 4.7 + GDExtension + libgr2 wired up (macOS)

- extension/: godot-cpp submodule (master, API 4.7), Metin2Model node
  registered, links xrender-poc/libgr2 via sibling-dir reference.
- project/: Godot 4.7 project — orbit camera + DirectionalLight3D (shadows)
  + WorldEnvironment/procedural sky + placeholder cube; main.gd probes the
  extension and can run libgr2 on a real .gr2 (MTGODOT_PROBE_GR2).
- build.sh one-shot build into project/bin/.
- docs/GODOT-POC-PLAN.md (phased: Phase 1 macOS -> M0'/M1/M2/M2.5).

Verified on this machine:
  [mtgodot] Metin2Model registered OK — libgr2 linked
  probe_gr2(warrior_cheongrin.gr2) -> gr2 OK: format_version=6 sections=8
  Metal Forward+ renders the scene (test/golden/m0-scaffold.png).

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WaHYEY9rwLWt21PULiYjeJ

extension/CMakeLists.txt

@@ -0,0 +1,37 @@
+# mtgodot GDExtension — M0' skeleton (registers Metin2Model, links libgr2).
+
+# --- godot-cpp (submodule @ master) ---
+# master has no per-minor branch; it ships bundled extension_api-4-*.json.
+# Pin to 4.7 to match the installed editor (4.7.1; patch-level ABI is compatible).
+set(GODOTCPP_API_VERSION "4.7" CACHE STRING "Target Godot API version" FORCE)
+add_subdirectory(godot-cpp)
+
+# --- libgr2 from the sibling xrender-poc repo ---
+# M0': plain sibling-directory reference (both repos live under .../mt/).
+# For a portable checkout, either git-submodule xrender-poc or vendor libgr2,
+# then pass -DXRENDER_POC_DIR=/path/to/xrender-poc.
+set(XRENDER_POC_DIR "${CMAKE_CURRENT_SOURCE_DIR}/../../xrender-poc"
+    CACHE PATH "Path to the xrender-poc repo (provides libgr2)")
+if(NOT EXISTS "${XRENDER_POC_DIR}/libgr2/CMakeLists.txt")
+    message(FATAL_ERROR
+        "libgr2 not found at '${XRENDER_POC_DIR}/libgr2'. "
+        "Pass -DXRENDER_POC_DIR=/path/to/xrender-poc")
+endif()
+add_subdirectory("${XRENDER_POC_DIR}/libgr2" "${CMAKE_CURRENT_BINARY_DIR}/libgr2")
+
+# --- the extension shared library ---
+add_library(mtgodot SHARED
+    src/register_types.cpp
+    src/metin2_model.cpp
+)
+target_compile_features(mtgodot PRIVATE cxx_std_20)
+target_link_libraries(mtgodot PRIVATE godot::cpp xrender::libgr2)
+
+# Drop the dylib straight into the Godot project where the .gdextension expects it:
+#   project/bin/libmtgodot.macos.template_debug.dylib   (Debug)
+#   project/bin/libmtgodot.macos.template_release.dylib (Release)
+set_target_properties(mtgodot PROPERTIES
+    PREFIX "lib"
+    OUTPUT_NAME "mtgodot.macos.$<IF:$<CONFIG:Release>,template_release,template_debug>"
+    LIBRARY_OUTPUT_DIRECTORY "${CMAKE_SOURCE_DIR}/project/bin"
+)