layout: restructure into src/ tests/ android/ scripts/ tools/

- extension/src/{port,platform,codepage} -> src/; native_render -> src/host
  (+ dxt, shaders/); libgr2 -> src/gr2; extension/third_party -> third_party
- extension/tests -> tests/port, libgr2/tests -> tests/gr2
- android-native -> android (build.sh, push-client.sh moved in)
- script -> scripts; tools/40250 -> tools/server; oracle -> tools/granny-oracle;
  perf tools -> tools/perf
- all build trees under build/ (native, release, android, port-gate)
- xrender:: CMake aliases -> mt::; port-map ledger impl paths rewritten

No code changes. ctest 15/15, port_gate macos+android PASS, port_map check 0 errors.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

CMakeLists.txt

@@ -16,11 +16,11 @@ option(MT_BUILD_TOOLS "Build libgr2 validation tools" OFF)
 option(MT_BUILD_PORT "Build the 40250 port and its tests" ON)
 option(MT_BUILD_NATIVE_RENDER "Build the SDL3 and Vulkan client" OFF)
 
-add_subdirectory(libgr2)
-add_subdirectory(extension/third_party)
-add_subdirectory(extension/src/codepage)
+add_subdirectory(src/gr2)
+add_subdirectory(third_party)
+add_subdirectory(src/codepage)
 if(MT_BUILD_PORT OR MT_BUILD_NATIVE_RENDER)
-    add_subdirectory(extension/src/port)
+    add_subdirectory(src/port)
 endif()
 
 if(MT_BUILD_TOOLS)
@@ -28,5 +28,5 @@ if(MT_BUILD_TOOLS)
 endif()
 
 if(MT_BUILD_NATIVE_RENDER)
-    add_subdirectory(native_render)
+    add_subdirectory(src/host)
 endif()