fix(codex): skip bash-only write gate on Windows

[Classy-Bear]

Summary

• add a Windows-specific command override for the PostHog PreToolUse write gate
• skip the Bash-only gate on Windows Codex, matching the gate script's existing Codex early-exit behavior
• add a regression test for the hook configuration

Why

On Windows, Codex attempts to launch hooks/gate-exec-write.sh before the script can inspect PLUGIN_ROOT and take its intended Codex no-op path. Depending on shell resolution, that surfaces as:

PreToolUse hook (failed)
hook exited with code 1

The script already deliberately exits successfully under Codex because Codex uses its own approval flow and does not support the hook's permissionDecision: ask response. commandWindows makes that no-op explicit and avoids requiring Bash just to reach the early exit. Claude Code and non-Windows behavior remain unchanged.

Related: #115 proposes a dedicated Codex approval hook. This change is a narrow fix for the current hook configuration and Windows installations.

Validation

• Windows Codex 0.144.1 live smoke: PreToolUse Completed, followed by a successful PostHog MCP exec call
• tests/test_gate_exec_write.sh: 45 passed
• Python suite including the new config regression: 72 passed
• JSON parse and git diff --check: passed