port 2D steps 3-4: strict 40250 asset gate with a provenance manifest

tools/asset_manifest.py records path/size/sha256 of pack/Index, every .eix/.epk
and Eternexus/root/*.msm (audit/assets/40250-client.json). The gate script sets
MT_ASSETS_STRICT=1, verifies the manifest, runs the native pack/proto tests and
four Godot tests, and fails on a missing client, a mismatch or a skip.
MT_40250_CLIENT now comes from the environment for the native tests too.
remote_player_test accepts both weighted WAIT variants (wait/wait_1).
PORT-PLAN §5 records the 2D status.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

extension/src/port/CMakeLists.txt

@@ -140,7 +140,10 @@ if(BUILD_TESTING AND CMAKE_SYSTEM_NAME STREQUAL CMAKE_HOST_SYSTEM_NAME)
 
     # Against the real 40250 Client/pack next to the reference source; skipped (77) when it is missing,
     # failed instead under MT_ASSETS_STRICT=1.
-    set(MT_40250_CLIENT "${MT_40250_SOURCE}/../../Client" CACHE PATH "40250 Client directory (pack/, Eternexus/)")
+    set(MT_40250_CLIENT "$ENV{MT_40250_CLIENT}" CACHE PATH "40250 Client directory (pack/, Eternexus/)")
+    if(NOT MT_40250_CLIENT)
+        set(MT_40250_CLIENT "${MT_40250_SOURCE}/../../Client")
+    endif()
     add_executable(port_eterpack_test ${CMAKE_CURRENT_SOURCE_DIR}/../../tests/port_eterpack_test.cpp)
     target_link_libraries(port_eterpack_test PRIVATE port_platform)
     add_test(NAME port.eterpack COMMAND $<TARGET_FILE:port_eterpack_test> ${MT_40250_CLIENT})