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>

docs/reference/DEMO-PLAN.md

@@ -54,7 +54,7 @@ xrender-poc/
   reuse/
     EterImageLib/      从 ../MobileSource 冻结拷入：DXTCImage.{h,cpp} + StdAfx + 依赖的最小集
     EterBase/          （拉伸）CFileBase / CMappedFile —— demo 初期可先用裸 fopen
-  libgr2/
+  src/gr2/
     include/gr2.h
     src/gr2_file.cpp        header + section table + fixup 重定位
     src/gr2_typetree.cpp    自描述 data_type_definition 遍历器
@@ -82,7 +82,7 @@ xrender-poc/
       compile.cmake       shaderc → metal + bin2c
   tools/
     gr2dump/main.cpp      CLI：结构化 dump + glTF 导出
-  oracle/                 Windows-only，见 PLAN §07（demo 阶段可先跳，用 Blender io_scene_gr2 当参照）
+  tools/granny-oracle/                 Windows-only，见 PLAN §07（demo 阶段可先跳，用 Blender io_scene_gr2 当参照）
   cmake/
     macos.cmake
   CMakeLists.txt