[codex] Add MetaTrader path discovery helpers

[NewYaroslav]

Summary

Adds reusable MetaTrader path discovery helpers and tidies the MetaTrader file-transport header surface:

• resolves the default MetaQuotes roaming/Common Files roots through optionx::utils::metatrader;
• uses Windows known-folder APIs first and a Unicode-safe wide %APPDATA% fallback when needed;
• exposes result APIs for default path resolution, terminal discovery, and MQL Files directory lookup so callers can distinguish an empty result from filesystem/path-resolution errors;
• discovers terminal data directories by MQL4/MQL5 folders and exposes their Files paths;
• records the first discovery error path while continuing past problematic child entries when safe;
• rejects symlink/reparse-point terminal and MQL child directories during discovery instead of following them outside the MetaQuotes tree;
• moves MetaTrader file-transport path/id validation helpers out of MetaTraderFileBridgeConfig.hpp into MetaTraderFilePathUtils.hpp;
• keeps bridge-family leaf/detail headers behind the bridges/metatrader_file.hpp umbrella include context;
• wires the utility into utils.hpp and the MetaTrader file bridge umbrella/config default root;
• adds a focused Windows Smoke workflow for MetaTrader file/path tests;
• keeps metatrader_paths_test lightweight by default, while the focused Windows Smoke workflow explicitly enables lightweight bridge smoke linking to avoid unrelated network dependency failures;
• enables MSVC /Zc:__cplusplus and NOMINMAX so dependency/header builds see the real C++ standard level and avoid Windows min/max macros;
• updates the EN/RU file-transport draft and build guide.

The concrete polling bridge class, terminal-discovery integration into that class, and MQL sample code remain intentionally out of scope for the next implementation PR.

Validation

• cmake -S . -B build-codex-pr68-mingw -DOPTIONX_BUILD_TESTS=ON -DOPTIONX_DEPS_BUILD_DIR=build-codex-pr68-mingw
• cmake --build build-codex-pr68-mingw --target metatrader_paths_test metatrader_file_config_include_test metatrader_file_bridge_test bridge_umbrella_include_test -j2
• ./build-codex-pr68-mingw/metatrader_paths_test.exe
• ./build-codex-pr68-mingw/metatrader_file_config_include_test.exe
• ./build-codex-pr68-mingw/metatrader_file_bridge_test.exe
• ./build-codex-pr68-mingw/bridge_umbrella_include_test.exe
• git diff --check
• cmake --build build-codex-submodule-consumer --target optionx_submodule_consumer
• ./build-codex-submodule-consumer/optionx_submodule_consumer.exe