Merge PR #7: Codex support (avidspartan1)

Adds the Codex adapter: marketplace.json, .codex-plugin/plugin.json,
declarative hooks.json with Windows command variants, and a shared
hooks/ponytail-runtime.js that switches state path and output format
between Claude and Codex (gated on PLUGIN_DATA, so the Claude path is
unchanged). Bumps plugin version to 4.1.0 and ships tests/hooks.test.js.

README adapters block resolved to keep the Codex @ponytail invocation note
together with Kiro (#6) and the drift-check Development section (#3).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

README.md

@@ -56,15 +56,30 @@ Lazy, not negligent: trust-boundary validation, data-loss handling, security, an
 
 The most effort ponytail will ever ask of you:
 
+### Claude Code
+
 ```
 /plugin marketplace add DietrichGebert/ponytail
 /plugin install ponytail@ponytail
 ```
 
+### Codex
+
+```bash
+codex plugin marketplace add DietrichGebert/ponytail
+codex
+```
+
+Open `/plugins`, select the Ponytail marketplace, and install Ponytail. Then
+open `/hooks`, review and trust its two lifecycle hooks, and start a new thread.
+
 That was it. He'd be proud. He won't say it.
 
 Active every session. `/ponytail-review` finds what to delete in your diff. `/ponytail ultra` exists for when the codebase has wronged you personally. `/ponytail-help` explains the rest.
 
+In Codex, invoke the skills as `@ponytail`, `@ponytail-review`, and
+`@ponytail-help`. Startup and mode-change text shows the current mode.
+
 Cursor, Windsurf, Cline, Copilot, Aider, Kiro: copy the matching rules file from this repo ([`.cursor/rules/`](.cursor/rules/), [`.windsurf/rules/`](.windsurf/rules/), [`.clinerules/`](.clinerules/), [`.github/copilot-instructions.md`](.github/copilot-instructions.md), [`AGENTS.md`](AGENTS.md), [`.kiro/steering/`](.kiro/steering/)).
 
 Kiro: copy `.kiro/steering/ponytail.md` to `~/.kiro/steering/` (global) or `.kiro/steering/` in your project.