feat: promote codex-rescue to ~/.claude/agents/ at setup time to support permissionMode

Problem

Plugin subagents cannot use permissionMode — Claude Code intentionally ignores it for security reasons. This
means codex:codex-rescue cannot get Bash permission in background mode, where permission prompts are impossible
and auto-denied.

Related bug: #94

Proposed Solution

Update /codex:setup to copy plugins/codex/agents/codex-rescue.md into ~/.claude/agents/ with permissionMode: bypassPermissions added.

Regular agents in ~/.claude/agents/ fully support permissionMode, so the subagent would work correctly in background mode after setup.

Changes needed

1. scripts/codex-companion.mjs — setup command copies the agent file to ~/.claude/agents/codex-rescue.md with
   permissionMode: bypassPermissions injected
2. Add a version/hash check so re-running /codex:setup after a plugin update refreshes the copied file
   automatically
3. /codex:setup output informs the user the agent was installed to ~/.claude/agents/

Tradeoff

Requires the user to run /codex:setup once to get the fix. Anyone who skips setup still has the broken plugin subagent.

Start in scripts/codex-companion.mjs at the /codex:setup command and inspect plugins/codex/agents/codex-rescue.md as the source file. Implement the setup copy with the requested permissionMode, refresh it when the plugin version or hash changes, and update setup output to report the installation path. Done means rerunning setup installs or refreshes ~/.claude/agents/codex-rescue.md correctly.