[codex] polish POSIX signal wake follow-up

[LimiNode]

Summary

Small follow-up polish for the POSIX signal wake service review notes.

What Changed

• Reset PosixSignalWakeComponent's shared service pointer before stopping the service.
• Added a comment explaining why the signal wake fd is stored as sig_atomic_t.
• Cleaned up the Russian README wording around the opt-in self-pipe wake component.

Validation

• cmake --build tmp/agent-work/build-runner-mingw --target test_console_application_runner test_loop_throttle_component --parallel 1
• ctest --test-dir tmp/agent-work/build-runner-mingw -R "test_console_application_runner|test_loop_throttle_component" --output-on-failure -> 2/2 passed
• cmake --build tmp/agent-work/build-runner-cxx11-mingw --target test_console_application_runner test_loop_throttle_component --parallel 1
• ctest --test-dir tmp/agent-work/build-runner-cxx11-mingw -R "test_console_application_runner|test_loop_throttle_component" --output-on-failure -> 2/2 passed
• rg -n '^\\s*#include .*\\.\\./' include -> no matches
• git diff --check