[codex] add POSIX signal wake service

[LimiNode]

Summary

Adds an opt-in POSIX self-pipe wake bridge so SIGINT/SIGTERM can wake throttled Consolix polling loops without doing mutex or condition-variable work inside a signal handler.

What Changed

• Added PosixSignalWakeService in core.
  • Maintains a self-pipe and watcher thread on POSIX platforms.
  • Exposes an async-signal-safe hook used by the existing runner signal handler.
  • Wakes LoopWakeService from ordinary C++ code after the signal handler writes to the pipe.
  • Compiles as a no-op on Windows.
• Added PosixSignalWakeComponent in components.
  • Starts/stops the service through the existing component lifecycle.
  • Lets applications opt in with consolix::add<consolix::PosixSignalWakeComponent>().
• Kept ConsoleApplicationRunner as the owner of POSIX signal handler registration.
  • The handler still stores the signal in sig_atomic_t.
  • When the opt-in service is active, it also writes one byte to the self-pipe.
• Extended the POSIX shutdown test with a long LoopThrottleComponent delay so Linux/macOS CI verifies that SIGINT/SIGTERM interrupts the throttle wait quickly.
• Documented the opt-in component in README, README-RU, and Doxygen mainpage docs.

Why

The previous runner behavior was intentionally async-signal-safe on POSIX, but a long LoopThrottleComponent delay could postpone SIGINT/SIGTERM handling until the throttle wait ended.

The self-pipe bridge keeps the unsafe work out of the signal handler while still waking the polling loop promptly. The runner signal handler writes one byte to a pipe, and the watcher thread wakes LoopWakeService, allowing the normal runner loop to observe the already-recorded stop request.

Validation

• cmake --build tmp/agent-work/build-runner-mingw --parallel 1
• ctest --test-dir tmp/agent-work/build-runner-mingw --output-on-failure -> 7/7 passed
• cmake --build tmp/agent-work/build-runner-cxx11-mingw --parallel 1
• ctest --test-dir tmp/agent-work/build-runner-cxx11-mingw --output-on-failure -> 5/5 passed
• rg -n '^\\s*#include .*\\.\\./' include -> no matches
• git diff --cached --check

POSIX self-pipe behavior is covered by tests/test_posix_signal_shutdown.cpp and is expected to run in Linux/macOS CI.