feat(codex): add Windows support and compatibility for Codex plugin

[SparshGarg999]

Root Cause

The Codex integration for skillopt-sleep was previously designed primarily for Unix-like environments, using bash runner scripts (run-sleep.sh), unix-style mkdir -p directory creation in the scheduler, shell profile export paths, and a Unix bash installer (install.sh). This caused installation and execution to fail when running under Windows CMD or PowerShell. Additionally, the Codex CLI backend did not support Windows-style tool shims (.cmd), unlike the Copilot backend.

Solution

This PR adds comprehensive Windows compatibility and support for the Codex plugin:

1. Added Windows Install/Runner Scripts:
   • plugins/codex/install.ps1: A PowerShell installer for Windows that replicates the exact logic of install.sh (copies skill files, retires legacy prompts, and suggests User-level environment variable setup).
   • plugins/run-sleep.cmd: A CMD runner wrapper.
   • plugins/run-sleep.ps1: A PowerShell runner wrapper.
2. Exposed Windows execution steps:
   • Updated the Codex skill definition plugins/codex/skills/skillopt-sleep/SKILL.md to include Windows CMD and PowerShell commands, allowing Codex to run correctly in Windows terminals.
   • Updated plugins/codex/README.md with Windows installation instructions.
3. Cross-Platform Backend Shims:
   • Updated resolve_codex_path in skillopt_sleep/backend.py to search Windows global Node/npm/NVM directories (e.g. %APPDATA%\npm\codex.cmd).
   • Updated CodexCliBackend.attempt_with_tools in skillopt_sleep/backend.py to write Windows-style .cmd tool shims when running on Windows (os.name == "nt").
4. Scheduler Portability:
   • Updated _runner_cmd in skillopt_sleep/scheduler.py to produce a Windows CMD-compatible directory creation and launch string when sys.platform == "win32".

Files Changed

• plugins/codex/README.md
• plugins/codex/skills/skillopt-sleep/SKILL.md
• skillopt_sleep/backend.py
• skillopt_sleep/scheduler.py
• tests/test_sleep_engine.py
• plugins/codex/install.ps1 (NEW)
• plugins/run-sleep.cmd (NEW)
• plugins/run-sleep.ps1 (NEW)

Testing/Benchmark Performed

1. Added unit tests test_codex_resolve_path_windows and test_codex_attempt_with_tools_windows to tests/test_sleep_engine.py to verify path resolution and .cmd shim generation.
2. Normalized unix/windows path formats in test_sleep_engine.py to ensure cross-platform test parity.
3. Successfully ran the entire core sleep engine test suite:

   python -m pytest tests/test_sleep_engine.py tests/test_json_utils.py tests/test_mcp_schema.py tests/test_plugin_sync.py tests/test_types.py

   (129 passed, 4 skipped)
4. Ran the deterministic sleep experiment locally to verify improvements:

   python -m skillopt_sleep.experiments.run_experiment --persona researcher --assert-improves

   (PASS: lift +0.6667, gate blocks harmful edits)

Fixes #46