Add Codex plugin manifest and setup skill

Author: ndycode

.codex-plugin/plugin.json

@@ -0,0 +1,6 @@
+{
+  "name": "oc-chatgpt-multi-auth",
+  "version": "5.4.9",
+  "description": "Install and operate oc-chatgpt-multi-auth for OpenCode with ChatGPT Plus/Pro OAuth, GPT-5 and Codex model presets, and multi-account failover.",
+  "skills": "./skills/"
+}

skills/oc-chatgpt-setup/SKILL.md

@@ -0,0 +1,51 @@
+---
+name: oc-chatgpt-setup
+description: Install or refresh oc-chatgpt-multi-auth in OpenCode, choose the right config mode, and verify ChatGPT Plus or Pro OAuth login.
+---
+
+# oc-chatgpt-setup
+
+Use this skill when the user wants to install, reinstall, upgrade, or troubleshoot `oc-chatgpt-multi-auth` in OpenCode.
+
+## Default install
+
+```bash
+npx -y oc-chatgpt-multi-auth@latest
+```
+
+Use this when the user wants the full catalog config, including base entries like `gpt-5.4` and preset entries like `gpt-5.4-high`.
+
+## Modern compact install
+
+```bash
+npx -y oc-chatgpt-multi-auth@latest --modern
+```
+
+Use this on OpenCode `v1.0.210+` when the user wants the compact variant-based config.
+
+## Login and verification
+
+1. Run `opencode auth login`.
+2. Run a quick verification request:
+
+```bash
+opencode run "Explain this repository" --model=openai/gpt-5.4 --variant=medium
+```
+
+3. For a Codex-focused workflow, try:
+
+```bash
+opencode run "Refactor the retry logic and update the tests" --model=openai/gpt-5-codex --variant=high
+```
+
+## Troubleshooting
+
+- Confirm `"plugin": ["oc-chatgpt-multi-auth"]` is present in the OpenCode config.
+- Re-run `opencode auth login` if tokens expired or the wrong workspace was selected.
+- Inspect `~/.opencode/logs/codex-plugin/` after a failed request.
+- Set `ENABLE_PLUGIN_REQUEST_LOGGING=1` for deeper request logging.
+- For full docs, see `docs/getting-started.md`, `docs/configuration.md`, `docs/troubleshooting.md`, and `docs/faq.md`.
+
+## Usage boundaries
+
+This project is for personal development use with your own ChatGPT Plus or Pro subscription. For production or shared services, prefer the OpenAI Platform API.