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

[fcsouza]

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.