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>

audit/contracts/world.environment-weather.md

@@ -52,7 +52,7 @@
 - `project/skybox_test.gd`：通过；CapeDragonHead/DawnMistWood texture-mode 六面天空、云层、scale 和 UV speed 断言通过。
 - `project/p9_test.gd`：通过；通用 weather snow/rain/none 粒子开关路径通过，但不是参考雪环境池测试。
 - `project/test_weather_daynight_parity.gd`：22 passed、0 failed；仅覆盖 `WeatherDayNightSystem` helper 的默认时相、时间推进、天气预设和信号，不覆盖正式 GameScene 接入或 40250 `.msenv` 渲染。
-- `extension/tests/net_entity_test.cpp` / `build/extension/net_entity_test`：通过；覆盖 `GC_CHAT/COMMAND` 的 `xmas_snow 1/0` typed event 顺序。
+- `tests/port/net_entity_test.cpp` / `build/extension/net_entity_test`：通过；覆盖 `GC_CHAT/COMMAND` 的 `xmas_snow 1/0` typed event 顺序。
 - `project/gamescene_test.gd`：通过；覆盖正式 GameScene 对 eligible map、四张 40250 排除地图和关闭命令的雪开关处理。
 - `project/netbridge_test.gd`：通过；确认 `M2Client.weather_changed` 信号已注册。