docs: make Codex workflows cross-platform

[cgfixit]

What

• Replace Codex-facing Bash-only bootstrap instructions with native Git steps that work from PowerShell or POSIX shells.
• Keep the existing POSIX optimizer harness available as an optional path.
• Record the current run_bot() live-mode hard stop in the money-mode skill.
• Clarify read-only versus explicit execution behavior in both updated skills.

Why

The existing Codex optimizer workflow required Bash, while this Windows Codex environment has no usable WSL Bash. The repository already has a PowerShell CI lint gate; the guidance now matches that supported path without changing trading code or safety logic.

Validation

• quick_validate.py .codex/skills/optimizer — pass
• quick_validate.py .codex/skills/optimize-money-mode — pass
• bash -n .codex/skills/optimizer/bootstrap.sh — pass
• git diff --check — pass
• Repo CI gates: ruff lint/format, mypy, and pytest passed through the repo preflight.

The preflight's regression-grep portion could not be trusted in this RTK/Git-Bash invocation because grep was unavailable; the change is docs-only and has no Python-file diff.

Risk to monitor

Docs-only. No runtime, configuration, live-trading, or risk-math behavior changes.