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/item.drop-pickup.md

@@ -73,7 +73,7 @@
 - `project/mob_death_drop_test.gd`：掉落坐标/地形高度、Yang 名称、拾取调用和死亡清理通过。
 - `project/p2b_test.gd`：掉落节点、proto 名称、多条名条去重、owner 独立名条和颜色通过，但退出仍有 2 个 ObjectDB 泄漏。
 - `project/text_tail_arrange_test.gd`：尾标 AABB 和 owner 排布通过。
-- `extension/tests/net_entity_test.cpp`、`extension/tests/net_classic_session_test.cpp`：ground add/del/owner 与经典物品包基础布局通过。
+- `tests/port/net_entity_test.cpp`、`tests/port/net_classic_session_test.cpp`：ground add/del/owner 与经典物品包基础布局通过。
 - 未覆盖：未知 vnum、真实 drop model/effect/sound、模型相交拾取、party + anti-flag 权限矩阵、observer/native action gate、CG_ITEM_PICKUP 后 GC_DEL→ITEM_GET/ITEM_SET 顺序、失败/重复/断线/换图竞态。
 
 ## Deep audit round 2026-09-20