port(2A): port/common Win32 layer, port_logic target and header gate

- Win32Types.h: fixed-width Win32 scalars, pointer-sized handles, static_asserts
- Win32Crt.{h,cpp}: MSVC _snprintf truncation contract, stricmp, timeGetTime wrap
- port_logic static lib linked into libmtgodot; standalone MTGODOT_BUILD_PORT build
- port_header_gate: every port/**.h compiles alone (twice) with its lib's
  40250 Distribute|Win32 defines (NDEBUG, USE_LOD, _DISTRIBUTE)
- script/port_gate.sh: macOS/Android/iOS/Windows(mingw) PASS, Linux BLOCKED

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

extension/CMakeLists.txt

@@ -56,6 +56,9 @@ target_include_directories(mtproto PUBLIC src/proto)
 target_link_libraries(mtproto PUBLIC mt3p::sodium mt3p::minilzo)
 target_compile_features(mtproto PUBLIC cxx_std_20)
 
+# --- port_logic: 40250 logic mirror (extension/src/port, docs/PORT-PLAN.md) ---
+add_subdirectory(src/port)
+
 # Host-only CLIs + tests: they run on the build machine, so skip them entirely
 # when cross-compiling the extension for a device.
 set(MT_HOST_BUILD FALSE)
@@ -186,7 +189,7 @@ add_library(mtgodot ${MT_LIB_KIND}
     src/proto/proto_node.cpp
 )
 target_compile_features(mtgodot PRIVATE cxx_std_20)
-target_link_libraries(mtgodot PRIVATE godot::cpp xrender::libgr2 xrender::formats mtnet mtproto)
+target_link_libraries(mtgodot PRIVATE godot::cpp xrender::libgr2 xrender::formats mtnet mtproto port_logic)
 
 # Godot's .gdextension expects, per platform:
 #   project/bin/libmtgodot.macos.template_{debug,release}.dylib