[codex] Add MetaTrader file command writer helpers

[NewYaroslav]

Summary

• add MetaTrader file command writer helper for signal.submit, trade.open, and account.balance.get
• add C++ smoke generator plus command-generation tests and CI coverage
• add reusable MQL4/MQL5 header and simple indicator examples that write commands through Common\Files
• document writer-side cleanup and MQL setup in EN/RU file transport guides

Local checks

• git diff --check
• cmake --build build-codex-pr68-mingw --target metatrader_file_command_writer_test -j 2
• cmake --build build-codex-pr68-mingw --target metatrader_file_command_writer_smoke -j 2
• cmake --build build-codex-pr68-mingw --target bridge_umbrella_include_test -j 2
• cmake --build build-codex-pr68-mingw --target metatrader_file_bridge_test -j 2
• ./build-codex-pr68-mingw/metatrader_file_command_writer_test.exe --gtest_brief=1
• ./build-codex-pr68-mingw/bridge_umbrella_include_test.exe --gtest_brief=1
• ./build-codex-pr68-mingw/metatrader_file_bridge_test.exe --gtest_brief=1
• ./build-codex-pr68-mingw/metatrader_file_command_writer_smoke.exe --self-test